Sounds like a bad preamp tube. You can pickup 12ax7's at your local music store. Buy one and replace V1. If the noise still persits then put the old tube back in V1 and swap the new tube into V2. There are only 3 preamp tubes in your amp. V1 is the one closest to the input jack, V2 is next and then V3 is last/furtherest from the input jack. Turn the amp off while replacing tubes.
That will be $59.95 please.
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