Low Frequency "Clipping"

hey all, I have a question that is driving me up the wall and I'm nearly at my wits end.
The problem is somewhat new. I am in the process of encoding records into Mp3's. The issue started a couple days ago when i started noticing a type of distortion on dynamic portions of "The Wall". It wasn't like the issues I've had in the past where there was way too much shimmer in the highs, but rather a sort of clipping (think of a blown or overdriven speaker) in the lows, typically in the kick drum portions. I have disassembled the system and tried to realign the cartridge (moving it further up and down the arm), reset the Anti-Skate, lightened the tracking force and of course tried other records, all with the same result "Clipping Bass". Does anyone know what this could be? The Cartridge (AT 71ELC or something like that) is only a couple months old with probably 150-200 hours on it. Does this sound like a cartridge issue (like broken) or setup error?
Any help would be great.

Thanks