Question:
Hey, i dunno if its supposed to be here lol anyway here goes.
My amp the Traynor YCV 40 is kinda doing its own tremolo. lol anyway the sound is kinda doin Wha wha etc and decrease. its weird i dunno if thats normal, or if its part of my weird guitar pick up problems. So ya..
Answer:
Is it after holding a note for awhile? If so, it's th attack of the sustain decaying.
Answer:
it could also be the reverb slowly dying out if your reverb is set really high.
Answer:
It may also be your power tubes. How long have you had the amp and when was the last tube replacement? Is the sound going between the speakers or is the problem exhibited equally in both speakers?