XV6700 + WM6, Phone keeps setting to "vibrate" mode

[DNeuwir]

Okay, I'm using an XV6700 that I've owned for a long time now, and I just upgraded to the WM6 in the "Helmi Official AKU 3.5 Kitchen, Release 1.0.4 (upd. 8/05/07)" thread.

While virtually everything is working great, I am noticing an odd quirk: I set the phone to a standard ringer, then, after some seemingly random amount of time (5 minutes up to a whole day), the ringer volume will switch on its own to "vibrate". This only happened since the upgrade--on 18+ months of ownership of this unit with WM5 I've never once seen it do that, but it's done it about 2-3 times a day for the past week just since the WM6 upgrade.

Is there some settting I've just got awry or is this a known issue?

Beyond that, I'm very impressed with WM6--it's about 50% faster (displaying tasks, contacts [I have 1800 contacts], etc) and web browsing appears to have somewhat improved performance as well.

But this one issue is driving me nuts...

Any ideas?