FINALLY, we have been able to reproduce this problem and figure it out. It is a problem that only affects the vintage compressor algorithm on Intel Macintosh platforms. The vintage compressor is included with TrackPlug and MultiDynamics. Symptoms of the problem include hearing mystery noises, loud oscillations, fullscale digital oscillation, and possible giant peaks (like 300 db). Really nasty stuff but not easily reproducible.
The problem was caused by a bug in the Mac XCode optimizing C compiler, generating a bad bit of code in a critical part of the compression algorithm. With the proper conditions this could cause a really large compression gain boost hence amplifying any low level noise to peak levels.
This will be fixed in the next release, which we will announce soon. Thanks for your patience, this was a very difficult and elusive bug.