Pick up the free
http://www.voxengo.com/product/span/ add it to an FX Chain module in the track/bus Pro Channel *after the EQ* and you'll be able to see the effects of what you're EQing.
Very handy.
Also, the Sonitus:fx EQ is another one to play around with.
Holding down the shift key will lock in the freq & gain of that node and mouse-dragging side-to-side will adjust the Q.
Play around with the different filter types - low/high pass, low/high shelf, peak/dip.
Generally, to locate offending frequencies, increase or decrease the gain all the way up/down & sweep back & forth till you hear the oddball frequency, then adjust the gain & Q.
SPAN will help you spot weird looking areas to check.