Someone tried to plug in an instrument to my Ampeg v4b while it was on and at volume. Made a loud noise (obviously) then wouldn't produce any sound. I turned it off and let it sit for about 20 mins and flipped it back on. Bass is coming through fine but theres this intermittent fluttery shushing sound. As if an instrument cable weren't making a good contact. Ive tried swapping out cables and another bass and its still there. Might be able to do a sound clip if that helps at all. Possibly a simple fix like swapping out tube? Would like to avoid taking it to an amp tech if it may not be too complicated. Any advice appreciated. Edit: Turned it on again to see whats up. After a couple mins of it being on, with my bass just sitting there untouched and volume down on it, the noise gradually comes in and then starts making the speakers bounce around as it gets louder. crackling and shushing.