I'm having a problem using my Virus B in multi mode with Sonar 4. I've got Vitar (Bank D #6

on channel 2 and Chrunchy (Bank E #

on channel 3. When channel 3 isn't muted, it changes the Vitar's sound (loud and nasty) and delay doesn't work for any of the parts.
When I mute channel 3, everything is fine. I tried putting the Chrunchy in a different track on a different channel and the same thing happens. If I change the patch on channel 3, there's no problem. If I have the Chrunchy sound in any channel it causes the problem - even when there are no notes or parameter changes in the track.
It was fine last night and I haven't changed anything... what's going on here?