Logic Pro 9 Omnisphere digital noise problem


I created a rhodes patch which has a nasty digital distortion and dropout.
I've sent the project to Spectrasonics, who can't hear a problem.

When I bounce a snippet, the bounce shows no artefacts. But if I record the audio using Audio Hijack, the distortion and dropout are evident.

The internal patch and the mixer track levels don't make a difference, the distortion is present with both brought right down.

No plugins on the track or on the master output.

What could cause distortion within a track that doesn't translate to a bounce?


PS: this is in Logic 9 and X.
: this also happens when I play live via controller kbd,
: same problem if I choose iMic for audio output.
: process and I/O buffer set to Max