Are you familliar with "sweeping" your EQ to find problem frequencies? If not, here's how you do it:
Set your EQ to a large (narrow) Q setting. If you don't have Q control, don't worry about it. Boost the EQ about 10 db. Now SLOWLY turn the frequency knob. Either start low and move high or start high and move low. Doesn't matter. When you come to the frequency setting where the mud (or silibance or whatever you're looking to eliminate) sounds the WORST, then you've found your problem frequency. Leave the frequency setting where it is, and change the 10 db boost into a cut. Cut only as much as you need to make the problem (mud or whatever) go away. This is also a good time to widen your Q if needed.