how to set up a tonearm/cartridge

I have a Micro Seiki RX500 TT, a SME 3012R arm, an Ortofon SPU Classic GME, and a Denon DL103-R cartridges, I'm having a distortion problem that I'd like some help with, if there a generous soul to point me in the right direction, please do so, I hear said distortion mostly when playing the last two or three tracks, and most noticeable when its a female singer.
Please help!!!
Thanks to all.
Mario