"MOTORBOATING"
Excessive feedback in an audio amplifier can result in a fluttering or popping sound that resembles the sound of a motorboat. This oscilation is caused by undesirable coupling between the output and the input of an amplifier or chain of amplifiers. It can also occur as a result of capacitive or inductive coupling in the wiring or be caused by the power supply. Because of the characteristic sound, this low-frequency oscilation is called motorboating.
This isn't the kind of feedback that made Jimi Hendrix famous. It may be that some of the point-to-point wiring in your amp is 'sharing' in ways that are not good for your sound.
