when I play my drum tracks (brush or normal) there is a lot of clicking and crackling and also some of the sounds are being repeated randomly at soft loudness, making a lot of uncontrolled noise.

I do have enough RAM and a fast CPU, so what might be the problem??

Dual 2.7 G5, 8 GB RAM, Logic 7.1.1, DIGI 002 with 512ms latency, JABB plugin.

Thank you very much for your help.