EXS 24 Logic Sampler Users Group

Hi everyone - 
I'm using LAP with the EXS Mark II and I get bad zipper noise
on samples and audio files when using the volume controller
(software or hardware, it makes no odds) but only between
midi values 90 - 110!!! Values 111-127 are fine and so are the 
values between 0 and 89.
I have a Hammerfall Multiface Soundcard I'm using the ASIO 
driver in a G4 single processor (867 MgHz)
Any ideas?