I have an Eastman upright, and just put a full circle pickup on it. Only yesterday did I have this problem. At band practice, with a practice amp, I was getting a lot of resonance/feedback on certain notes. Later that night, at a gig, it became full blown feedback. It really prevented me from getting the bass loud/eq'd enough. So, not sure what question to ask here, but could it have something to do with the age of the strings (as they sound a little muffled and I'm not sure how long they've been on) or something else? What steps to take with a new pickup/bass/cabinet combo (and nothing else like pedals)? Thanks!!!