Something is terribly wrong. Most records, used or otherwise sound fine. First thing is to do some tests. Reverse the leads on the phono input at the back of the MF. You said that the right channel was worse, if the left channel is now worse it is a table setup matter, if the right channel is still worse, your phono preamp has a problem. Check to make sure that the ground wire is solidly attached to the grounding screw. If it is the table, and you have verified correct tracking force, anti-skate and overhang then the next thing to do is screw with arm height. Lower the arm a very small amount at the pivot point and report your results. Finally, you might consider posting what city you live in and one of the sorry asses that spends too much time on this forum might be glad to help. Hell, if you live in Portland, OR I'll be over this evening. You buy the beer; I'll bring the records.
Marty
Marty