Keep us posted, I have a set of those monitors. If you have the same problem again I may take some preventive action on mine.

That's ridiculous! I'm sorry for your troubles. Please let us know what the problem was, and post more pictures!

UPDATE: So these speakers are about a gnat's butt away from going in the trash!  What a waste of $400, 3-1/2 years ago.
 
The other day, I opened up the speaker cases to investigate the new trouble.  One speaker had intermittent woofer operation, and the other speaker had static/crackling in the mid-range driver.  After some investigation, the IC amplifiers that power the units are TDA2052 (mid-range driver), and the TDA7296.  Both are 60W amplifiers, and I have no idea why KRK decided to use both at the same time.
 

 
Upon inspection, the TDA2052 was outputting about 200mV DC to the mid-range driver.  Not good.  It should be zero.  When the DC was "on the line", the speaker crackled and popped.  However, as the unit remained on after about 5 minutes, the crackles and pops subsided.  It was noted at this point in time that the DC was near-zero.  This screamed amplifier IC failure, so I immediately sought replacements.
 
After receiving the new components, I unsoldered the amplifier and replaced the old with the new.  Upon power up, the speaker did not work as expected.  The mid-range driver did not work.  When powered up, I observed some very quiet sizzling on the board!  WTH?!?!?  This was nowhere near the amplifier IC's.  It turns out that the black "goop" near the higher-voltage (+/-20Vdc) capacitors was sizzling!  I could see tiny bubble emitting from goop!  So what's this "goop" I speak of?  Well, it's like a glue that the jerk manufacturers sloughed all over the board to hold components and wires in place.  It turns out that this stuff was conductive.  Not good at all.
 

 
I managed to remove some of the goop and eliminated the sizzling.
 
However, at this point in time, the new TDA2052 was outputting 11V to the mid-range driver.  Again, not good.  Near this amplifier was more goop, that spanned a jumper and a resistor.  I cleaned up the goop as best as I could, and I noted the 11V dropped to about 10V.  So I continued to clean up more goop, but the voltage did not reduce any further.
 
Thinking the replacement TDA2052 was shot, I swapped it out with another (as I bought two of each amplifier IC).  Upon power up, the output to the mid-range driver was 0V.  Yeah!
 
All good, until the replacement TDA2052 let out it's magic smoke!
 
So there you go.  The black goop coats the circuit board in many places, most likely conducting and corroding where it shouldn't.  Overall, these speakers were doomed to fail since the date of manufacture.
 
I may try to clean up and put the other amplifier (i.e. the first swap-out) back in, but I'm not getting my hopes up.
 
I'll continue to update the thread as things progress further.
 
 

Hey, down there in the valley. Greetings from up the hill!
 
Sorry for your troubles. I go back to discrete component days (designed solar-powered SCADA systems). Gotta say that I don't miss it. Don't miss programming in assembler, either. 
 
This whole Series of Unfortunate Events reeks of poor design margin. And cheap capacitors. Or expensive capacitors with flawed subcomponent(s). I had an issue once where new production of a very reliable product started failing in the oil fields (not a good place for failures; I never blew ANYTHING up; those bastidges at BP who bought out Amoco can rot in hell). After MUCH investigation and finger-pointing, it turned out that the Level-2 supplier of the tantalum powder to the capacitor manufacturer changes sources and failed to inform their customer (my supplier) of the change.
 
Could be something foreign in the goop. Or picked up from moisture/humidity over time.
 
Sorry you've been slimed.
 
I'm happy the only sound coming out of my BX8 D2's is very low level 60 Hz hum. So are my dogs. They're still sleeping. 
 
Edit: Hey, when you lived in NW IN, did you ever get a chance to visit the Sweetwater store? One of these days, I want to pack up my dogs (including the one that gets car sick, and take a nostalgia trip on the Mother Road (the hospital I was born in had a Rte. 66 address!)) and go visit that store. With a couple of credit cards. And debit cards. And GAS!

TheMaartian
Hey, down there in the valley. Greetings from up the hill!

 
Greetings!  Brrr, it be cold up in dem hills!  It was 62 this morning with a nice breeze.  Since I was up early before the sunrise, I enjoyed the morning coffee out on the lounge chair gazing up at the stars.  I'm definitely liking the cooler weather but miss the heat in a way.  Yeah I know, I'm crazy!  Back in Indiana, it's 32 with a butt load of snow coming--no thanks!
 

TheMaartianSorry for your troubles. I go back to discrete component days (designed solar-powered SCADA systems). Gotta say that I don't miss it. Don't miss programming in assembler, either. 
 
This whole Series of Unfortunate Events reeks of poor design margin. And cheap capacitors. Or expensive capacitors with flawed subcomponent(s). I had an issue once where new production of a very reliable product started failing in the oil fields (not a good place for failures; I never blew ANYTHING up; those bastidges at BP who bought out Amoco can rot in hell). After MUCH investigation and finger-pointing, it turned out that the Level-2 supplier of the tantalum powder to the capacitor manufacturer changes sources and failed to inform their customer (my supplier) of the change.
 
Could be something foreign in the goop. Or picked up from moisture/humidity over time.
 
Sorry you've been slimed.

 
The Amoco vs. BP thing is/was a huge deal back where I was from.  One of the country's largest refineries (Whiting) was near where I lived.  Not sure if things changed much when BP took over, but Amoco was a the all-American pride of the oil industry I'm sure.  Corporate buy-outs/take-overs don't come easy when it's a bunch of ferreners!
 
GOOD NEWS ABOUT THE SPEAKERS: I may have rectified the situation with the smoked speaker.  After swapping out the torched TDA2052 with the original IC, it seems to be working again.  So maybe the original was okay, but the good was affecting it.  More tests to follow.
 
So that means for the other speaker, I intend to clean up the goop first before swapping out components.  We'll see how that goes.
 

TheMaartianEdit: Hey, when you lived in NW IN, did you ever get a chance to visit the Sweetwater store? One of these days, I want to pack up my dogs (including the one that gets car sick, and take a nostalgia trip on the Mother Road (the hospital I was born in had a Rte. 66 address!)) and go visit that store. With a couple of credit cards. And debit cards. And GAS!

 
I never did visit the store, though I wanted to.  In fact, I never visited Fort Wayne the entire time I lived in Indiana!  It was pretty far from where I lived, but I was out that way one day for work on my way to the booming metropolis of Waterloo IN, and I drove past the store.  It was BIG!  At first I thought it was one of those warehouse/truck depots until I saw the sign.  I should have stopped in, but I needed to remain on schedule.
 
As for Route 66 goes, that sounds like an interesting trip, but I think the fun Route 66 stuff is here in the Southwest/West.  There's more of that nostalgic feel to it.  Maybe it's the desert/mountains, maybe it's the nice weather, maybe it's the open roads, or maybe it's a little of everything.  That and dinosaur statues!

hey man,
thanks for posting this, same thing happend to me today.
 
can you post a link to the  2.2kΩ, 1/2W carbon film resistors that you got from digi?
dont know which one to buy
thanks!!

dvdxyan
hey man,
thanks for posting this, same thing happend to me today.
 
can you post a link to the  2.2kΩ, 1/2W carbon film resistors that you got from digi?
dont know which one to buy
thanks!!

These speakers suck.  As I mess around with them more and more, the build quality of the board and mounting hardware is kinda bad.
 
http://www.digikey.com/product-detail/en/CFR-50JB-52-2K2/2.2KH-ND/665

i know,but what can we do.. we already wasted the money on this junk
thanks!

dvdxyan
i know,but what can we do.. we already wasted the money on this junk
thanks!

 
True.

Well, it's all in the goop!  Thank you KRK manufacturing team for the Black Goop of Death!
 
Speaker #2 repaired without replacing any components...well, at least not the amplifiers!
 
Check it out.  I encourage all those who are repairing their Rokits to clean out the goop between components.  Seriously, this stuff makes a complete mess.  It hard and you must either chisel it out or find another means.  Rubbing alcohol doesn't seem to penetrate the stuff, but it does clean up the area after it has been removed.  Acetone may prove to be more effective.
 
Location of previous repair last year, the replacement of the 2.2k ohm resistor, which was cooked.  But note the corrosion of the jumpers.  I replaced the capacitors (removed) in this area as well, as they both were bulged and had failed.  The goop got 'em!

 
All cleaned up and much better!

 
Another area that was cleaned up.  This area also sees raised voltage levels (+/-20V) and the jumper and the components showed signs of corrosion.  I also replaced these capacitors as well (not shown).

 
After cleaning up all the areas shown above, the speaker turned on and sounded good!
 
So my advice?
 
1.  Check the boards for corrosion and areas where the Black Goop of Death covers multiple components, especially jumpers.
 
2.  Remove the BGoD using chemicals, a pick or X-Acto blade.  In my case, I used a hot soldering iron with a chisel tip + X-Acto + isopropyl alcohol.  If you use your soldering iron, then be sure to clean it well afterwards.
 
3.  Replace burnt resistors and bulged capacitors.  Overall, I think it's a good idea to replace all of the power capacitors.  The two in the middle are 1000uF 35V electrolytic caps.  I replaced them with 50V versions.