This question is already answered on the prior archived forums and I can't figure out how to post there. I had been experiencing sudden volume fluctuations while using my HD300 in a live setting, and could not figure out what was happening - I thought I had a defective unit.
Via a Google search, I found this on the old forums, posted by both Crusty Old Rocker, with the same information also posted by Spaceatl:
"Try this, rotate all your pots fully a dozen times, do this every now and then to keep them clear of any muck that might be getting in there. You will also notice that there is like a null area on each pot near zero and 100 percent. Once you have your settings assigned to your patches and don't need to make any adjustments while playing, you can "park" the knobs in that null area where they won't deliver a value change due to vibration."
I'm testing this solution now, but I'm fairly certain this is the issue. I am re-posting it on this new forum so that any searches for similar problems might come up I hope that re-posting the properly quoted content above isn't a problem for the original answer poster. I hope this helps others.
- Tom Hyzy