I have a residency at a live music pub in central Liverpool. It has a house PA that I go through with my U-Bass with Pyramid steel strings. However, I face a constant battle when playing straight into the desk in that one particular bass note (an F) results in a really loud booming, (almost feedback) which reverberates through the large room and if left unchecked results in feedback. Plus it makes it almost impossible to play smoothly as I'm constantly fighting the boom on F notes. I've taken ALL the bass and middle off the channel on the desk and all the bass off my bass but still get that boom. Plus the sound of the bass then is very toppy and I get an audible click when playing the strings that you can hear through the PA. I wondered if anyone could suggest way around the problem?