When i am palm muting notes on the low E and A strings, i keep getting this high pitched buzz/pinging sound. I thought it was the guitar, but i tried another guitar in the amp, and it still did it. Tried with another amp, and it was fine. It doesn't really sound like a blown speaker though.

The amp is a peavey VK head with a 412 kustom cab.

Any ideas as to what is going on? all the other sounds from it are ok. The clean channel is getting more and more distorted at high volumes though.

would this be a tube problem?

Thanx for any help.....
Dirty Sanchez