A few weeks ago I saw a ska/rock band in a small youth centre. The bassist was using a Titan V12, with a PH410 and PH115. The sound was pretty massive and bassy, probably more than enough for the room. The weirdest thing kept happening; whenever the bassist had a rest, the room was filled with a low pitched, wooly and very loud humming sound. The next band came on, with a bassist just as loud and this feedback stopped happening. A couple of weeks later in a similar small pub, the bassist was using a BB750 with a Mesa 410, and exactly the same thing was happening. Both of these bassists were using a Fender American Deluxe Pbass. (the one with the bridge soapbar) These are the only times I have ever heard bass feedback. Is this more common with meas heads? I didn't detect any distortion in either of the bassist's sounds, so they couldnt have had their gain set too high. Anyone know what was going on here?