My Hot Rod Deluxe is making a loud cracking noise in over drive. It's never done that before. The tone is brittle. Not good 

Could be many things. Is it only on the overdrive channel?
 
Hard to diagnose online, but not impossible.

 
Have you tried re-seating the tubes? Do you have electronics cleaner?
 
I have cured crackling problems before on my amp by pulling each tube, spraying each socket, and re-seating each tube while gently rocking them back and forth as I put them in.
 
It may have nothing to do with the issue but it is easy to try.
 
Good luck!

 
For a crackling noise the first thing I'd do is cycle the cord connections a few times to make sure the contacts are clean at the jacks and plugs.
 
Then I'd pull and re insert each tube just to make sure those contacts were clean.
 
If that didn't get rid of the crackling noise... I do a quick swap test with the phase driver/splitter/inverter tube... as a breakdown in that tube (one of the few tube positions where tube actually seems to wear out) can cause a crackling sound.
 
On the Hot Rod Deluxe this tube will be labeled V3.
 
If that doesn't help then I'd want to get more specific about what the word "crackling" is describing.
 
 
One possible clue is the "overdrive" channel. This might suggest that the problem is in the overdrive circuit... or it may suggest that the problem manifests itself when the overdrive causes extra vibration in the amp chassis and is in the general circuit.
 
Crackling is usually something simple... but it can be hard to locate.
 
 
 
best regards,
mike
 
 
 
 

I spray the pots on my guitar as well as the amp from time to time with some spray contact cleaner. Be careful not to get it on the finish of the guitar or anything else that will be easily damaged. On the guitar, I press the nozzle gently and have the finish protected,..... I dribble a few drops into the pot and work the knobs.
 
I work the pots back and forth till they move smoothly. Then I turn the amp on and work them as well. Dust and corrosion tend to get into the pots and they become harder to turn and they also get scratchy. If left that way, the static will come in to the sound as well..... not just when I make adjustments.   A few minutes to pull the amp apart and spray the pots clears that up..... both the stickiness and the static. 
 
The same thing happens in the tube sockets. Advice above is good.   check the tubes in the preamp stages for microphonic tendencies. I've had a few exhibit a buzzing at higher volume and on the distortion channel. I have mostly used combos so the speaker vibration gets right beck to the tubes as the entire cabinet vibrates.  Replace as needed.

There are three 12AX7s in that amp. Try swapping them around. Or gently tap each one while powered up and listen for noise. One or more of them may have become microphonic. If so, it's best to replace them all at the same time. And, as noted above, just pulling them out and re-seating them can sometimes remove oxidation from the pins.

I have a unique  suggestion.
 
Take out each tube and re-seat them.
 
{BB to Bapu} Thank you Captain Obvious
{Bapu to BB} Just doin' my part
 

Thanks so much for the responses. I screwed up by describing the sound as crackling. It's a sound I've never heard before but it's loud enough to be clearly heard. There seems to be some effect on the tone of the amp also. The bass control doesn't seem to have a lot of responsiveness as before and one thing I just thought of is there is crackling when nothing is being played and it's pretty loud. I will try the suggestions and thanks again for the help!!!

The second small tube from the far right of the chassis does double duty. It's the tone control make up stage and part of the drive circuit. This tube is the one that you should swap for a known good tube. There are a number of relays and solid state drive devices involved in the OD circuit also. It's important that you determine where the bad sound is. Normal, drive, more drive. If it is tied to one of these operating modes then it makes isolating the problem easier. It's very doubtful that it's a dirty pot or socket because those types of issues come and go. Also, if it was a pot you would hear the noise when turning it.

Thanks John. It's in the more drive channel and I have to crank the amp a bit for the sound to come out. I've been using each channel for distortion levels. Clean channel/ drive channel for crunch/ more drive for hard rockin. Songs like I can't get enough of your love in more drive. 1/3 of the repertoire is in more drive so this is quite a problem for me.