VIP 1 Weird volume drop (almost as if it's compressed)

[Surphyse]

I bought this amp a little over 6 months ago. It was brand new. Recently, I noticed the volume would randomly, not drop per say, but sound muted and compressed when playing on certain amps. It was first only on the 6505, then it became 6505 and 6534, then the XXX, and now, it seems to happen on the British amp as well. If it weren't for the 6534, I would've guessed it had something to do with which amps I use the most but I don't remember ever using the 6534. I tried calling Peavey and they said to call the local peavey repair center. I called my local authorized peavey repair center and they said without the receipt, I'm going to have to pay for repairing this 6-month old amp, which is ridiculous. How would I have known that the receipt is the warranty? But I digress.
To make sure it wasn't just my pups' battery running out of juice, I used a new battery. I then assumed the guitar wiring might be loose, so I used a different guitar that had passive pups. And to make sure it isn't the cable either, I used a new cable. This is definitely an amp problem because I only experience it on certain amps, not all of them.
Here's what it sounds like
***NOTE: LOWER YOUR VOLUME!***
http://puu.sh/bDuoi/294482f023.wma

[wmjones]

After listening to the sound drop and the sudden rise at the end, and the style of playing you need to check your speaker wire connections. And possibly other connections inside the chassis.
HAPPY DAYS

[Surphyse]

Would it really be the speaker connections? I have doubts about this because this only happens when using certain amps. For example, I've never experienced that on the Classic or the Budda. I'll definitely check the connections though. Thanks.