I have a Vetta II combo.  I was in the middle of a gig last night and all of a sudden the volume on a patch cut by at least 1/2.  I use the longboard and immediately punched in another sound, then went back to my original sound.  All was fine...until it happened a second, third and fouth time.  It did this on a couple of different patches.  Any help is greatly appreciated!  Hugh

I just had this problem: my patch volume was alternating between the patch volume setting and the knob setting. Vibration is blamed and it can happen to any of the patch setting knobs.

I zeroed out the patch adjustment knobs, turned them all the way to the left, and the problem stopped. Rubber gaskets are also suggested to stop the knob from vibrating.

Line 6 service said that the patch knobs are not actually potentiators, they're encoders and therefore much more sensitive to vibration.

check this posting for more details

http://line6.com/support/message/39647#39647