Decaying chord noise

[dcburn]

Loaded my 4x12 with new speakers Friday.
I guess I hadn't used my JTM45 much since I got my 18 watt back from Friedman.
I'm now noticing as the chord is decaying, at the bitter end there is sort of a farty sound. You really have to listen, but its there.
The amp volume is set around 6-7 on the high input and low is around 3-4, channels jumped. I'm using it with my PS-2.
Sounds like there's a little oscillation going on as well.

Could it be a filter cap or power tube issue?
Ive never changed tubs and have a bunch of pre amp tubes, so I started messing around with that.
Found one of the JJ's a little suspect looking. Replacing it didn't cure that noise though.

Did find I liked the JJ's better than EH 12ax7's and 7025's and TungSol 12ax7's.
But a TungSol 12ax7 in V1 really livened up the amp some.

 

[heinz_57]

Lightly tap the tubes with a pencil and see if they make any noise through the amp. I had an amp kill 2 preamp tubes at once so when I was rolling the new tube trough all the positions I couldn’t eliminate the problem. Wish I’d have known about the tapping trick then. Had to pay an amp tech to trouble shoot it. He told me about the tapping trick.

This may seem obvious, but if you are just playing in your house attempting to keep the volume down, Make sure the volume is not on the cusp of not making noise. That can definitely yield artifacts like you are describing.