Audio Channels Noise on Export

[Incredible_hand16B8]

Adaptive Audio Channels are causing noise on some clips upon export.

In the timeline they play back fine, as expected.

Upon export of the timeline, they give full scale, stuttering noise in the exported clip.

These are 4 channel clips in a 6 channel timeline.

In addition, what should be 6 audio channels in the timeline, appear to be only 4 channels in the "effects controls" window. I can re-edit the original media back into the timeline, and it appears as 6 channels. At some indeterminate point they start appearing as 4 channels once again. In the "effects controls" panel, these odd clips appear to have additional settings beside the "volume in" and "volume out" headings - they appear to be nul values for 6 channels.

Edited to correct: these are 4 channel clips in a 6 channel timeline.

To clarify - the channel settings are quite secondary to the issue of the very loud noise upon export. I posted details on those as they seem possibly correlated.

[Incredible_hand16B8]

Update: this problem may be exclusive to H264 exports. AIFFs and QTs seem not to have the audio issues.

[Incredible_hand16B8]

Screen Shots to illustrate channels behavior mentioned above.

1st - both "bad" and "good" 6 channel clips appear the same in the clip mixer (here with channels 3 and 4 down to minus infinity)
2nd - 4 channel clip showing normal with controls for all 6 timeline channels - no additional settings visible.
3rd - 4 channel clip showing only 4 channels in a 6 channel timeline - odd additional settings visible.