this only started to happen recently and only with my music man bongo. all other basses are fine. It is an active 4 string bass that takes 2 9v batteries. The amp is an ampeg SVt classic head (mos-fet) 350W Then i have that going through a 4X10 ampeg and 1X15 ampeg cab. I have had the amp for 7 years and never a problem until the bongo. I must always have the -20db on due to the amount of power the bass sends to the amp. I would usually have the gain half the amount of the master so that the amo is loud without clipping. It sounds great though i do wish i did not have to use the -20db button. Anyway, only recently has the bass cabs started to fart. no matter what level i have the amp head set to it just keeps farting. usually when i strike a string hard. Now i have replaced the batteries and done all the usual checks to see if it was the bass but it seems to be fine. I have played it through another amp and all. As for the cabs they work perfect with other guitars. So what i am asking is what could the problem be? very strange imho boggy.