Ste, the guitarist in my band has been using the Planet Waves tuner for a while with an adaptor, but last rehearsal, he used it with a battery and everytime he left it in his signal chain, there was this loud high pitched screeching. I don't know if that's the same as the noise you mentioned, but is there anyway to get rid of it? (appart from the obvious idea of not leaving it in the chain, or using a looper to mute it)