sporadic distortion in low end?

I have pretty cheap-o vinyl setup with a Music Hall MMF-2 and a Benz Micro MC20E2, and admittedly, don't know too much about this sort of stuff, but have been having a problem for months that I am just now getting around to dealing with.

On a few records of mine I am having problems with low-end distortion. The particular recordings I am having problems with have a really open kick drum, that when coupled with certain notes in the bass line produce a distortion so severe, it can skip the record. I can counteract this increasing the tracking force, but even when I get beyond what seems like a comfortable weight, it still distors, but doesn't skip. I don't have a stylus force gauge and set up the cartridge myself (although I had help and feel pretty confident that it is aligned properly).

Problem is that it is really sporadic. I have only noticed this on two different records (both by the same artist and pressed at the same plant), which almost leads me to believe that it could be a pressing flaw, but I feel like other people I know with the same record would have this problem (which they don't), and I don't remember having this problem when I had a basic technics/Audio Tecnica setup for records. And, most everything else I listen to sounds really good.

Any ideas? Maybe my cart is messed up? maybe I just need to get someone to professionally set up the cartridge? maybe the size of the cart screws up the VTA too much?

pablo