Akai S1000 / S1100 samplers

Hi all,

I get white noise distortion added to the samples on long release  
keygroups when more then 2 notes are played, is this a DAC calibration  
problem?
I've gone through the service manual but can't get the hardware test  
mode to activate, I'm on a S1100 v4.3 with 32mb memory.

any advice would be appreciated


Thanks

Gower