Well, this was mostly a guess, but try moving the amp to another room.What would be the solution? I'm moving soon and not sure what to look out for
Does it do it at all volume levels?
And of course, try a different bass, a different chord, plug it into an outlet in another room.
Has it ever sounded good and started sounding bad or is this a new thing?
How loud do you play it? Could the speaker be going out?
How old is the amp? I don't know that the current series (v3) included a 30. I know there is a 15, a 25, a 40, and so on.