I have not had this problem at all. Maybe if you posted more info, such as your computer specs, audio card, notation or sequencing software of choice, etc., someone could help you troubleshoot this. Good luck.
Make sure that the combination of instruments isn't causing your audio output to clip. It sounds like your audio is clipping. Check the outputs for each instrument in the Kontakt Player (while playing) and your sequencers mixing channels to see if you can find where the clipping is coming from. You may have to drop the overall dynamic level of some of the instruments to get the piece to play without clipping.
When I have many GPO instruments playing, I get tremendous distortion. At first, I thought I was overloading my playback system, but I've since discovered its not.
Anyone have experience with this?
Yes, I agree with Joseph. Ensure each channel has the appropriate level. Sometimes, the Kontakt player tends to clip if the levels are too high, especially if you have activated the Volume/Pan midi control (options menu).