Mixing your music - how do you handle interfering frequencies?

Hi again,  just mixing a new tune of mine, and finding my clean guitar track/main lick is "warbling" a bit against what seems to be the bass track. It may be the sum of the bass and drums and is subtle, but noticeable to my ear anyways. I'm having trouble finding exactly where the trouble is, and how to eliminate the problem interaction. 
1) Would you possibly be able to tell me how you would approach this sort of problem exactly, step by step?  Which tools exactly would you use?  I  just have whatever comes with Sonar Studio X3. 
2) How do you approach cleaning up / thinning out the mix so that it's not losing anything as far as quality of sound goes, but thins out the areas that seem a little too muddy or full? Looking for a very clean distinct yet full bodied end product. Not asking much for a newbie, huh? 
 
Appreciate all the help!

If you suspect frequencies are competing and your ears aren't helping you to find the problem, you can try a visual approach.
The QuadCurve or similar EQ will show you the full frequency spectrum of the signal being fed into it. Place an instance on each of your two tracks and look for the frequencies they have in common. Decide which instrument deserves that area of the spectrum and cut the other one by dialing in the Freq & Q and subtracting a few decibels. Keep the Q reasonably wide so you don't end up with surgical artifacts in the neighboring frequencies, but not so wide that you deaden the sound.
If the problem lies at the top end of the bass, and the low end of the guitar, you probably should just roll-off the frequencies above and below a certain threshold, as Zargg suggested. 

Wavefactory's TrackSpacer.
 
The easy but not cheap way of doing it.
 
You'll get no engineering degree from using it, but it can do the job nicely.

For me, MMultiAnalyser from Melda Productions tops the lot. Currently €59 / $65, although there are discount periods from time to time. 
 

Anderton
A little confused by your mentioning "warbling." Do you have any compression on the master bus?

Nothing on the master bus...  it's almost like a tremolo effect, kinda hard to hear, but subtly there. Comes out more prominently after converting to mp3 as well. 

I too have started using MMultianalyzer.  It does a great job of displaying conflicts. I think the tricky part for most people is making the choices to resolve the conflict. That rolloff that sounds good in the mix can sound very thin if the other sound it was layered with drops out.  Sometimes a notch approach is better

Oh ...making MP3s can be tricky...I do not go to zero on my mixes to mp3 but go upto -3 but not beyond , and cut the high and low eq ends  a bit / tail ends.(stops odd harmonics.especially on low bit renders of 64 bit or lower)...and it has to be mixed for that right, to get it good sounding...

konradh
Is it a slow cycle, like a phasing or comb-filtering sound, or is it fast?
 
I'm guessing you know what beats sound like when two sounds are slightly out of tune, right?  That's another thought.
 
Can you solo two sounds and hear it?

It's a fast tremolo effect...   it was doing just fine in the mix, and then something happened to create this new twist... perhaps just adding compression to the bass was enough to do it, I just have to get some more free time to get in there and sort it out.  At some point you start to wonder if you're hearing things...  but there's no doubt it appears in the mp3, and back-tracking it is there subtly in the mix.  Thanks for the idea about tuning...  
I had a similar thing happen on a different song with drums and bass, and had to de-resonate the drums a bit in Superior Drummer to fix the problem.