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.

See if it occurs with another source other than TT. If it doesn't, the problem lies in the turntable/TT setup. If it does, switch the right and left speaker cables to see if it still occurs, or if it changes with the speaker. If it changes with the speaker, than it's upstream electronics. If the same speaker distorts, you probably have a blown woofer. If it can be isolated to the upstream electronics, maybe just a bad tube. Knowing something about the rest of your system will help, but the above is a start.
Really sounds like tt set-up. Is everything ok thru digital front end?
Get more specific- tt-arm-phono stage, pre-amp, amp and speakers.

I have experienced the same thing when cart- arm -phono stage are out of whack as far as gain, set-up. Let's see what you have first and we can go from there.

The last time that occurred, I had to raise the VTA of my arm and it cleared up. I had the back end too low and my bass was starting to break up. Until we know what you have it's not clear if you can even change VTA.
Records into MP3's? Why?
Wow, thanks for all the responses. Well to answers everyone's similar question first.

The Digital side of my systems works perfectly. SACD, PC, DVD, CD even the MiniDisc I barely ever use any more all work fine.

If VTA is my issue, then I have no clue how to set that, and my latest hobby has taken a serious detour. I will dig deeper online to see if there is anything I can do for this setting.

And lastly, Q-"Records in MP3's?", A - I think I would look pretty stupid trying to get a Phono setup through a airport security checkpoint, Portability, why else?
This should help setting up your VTA:
TT Set-up