I'm a musician, not any kind of electronics engineer. I've had a Behringer Xenyx Q1002USB audio mixer for a couple of years. I bought it new. From the start, there was an audible buzz from it at all times, although it isn't present in the audio signal. The mixer has a separate mains transformer which doesn't buzz. Is there a relatively obvious reason for this buzz (Behringer is a low-cost company, with all its products made in China)? Is there also a relatively simple solution? I can use a soldering iron.