I know this is a bass forum but I'm hoping someone here can help me out. I just bought a new 15w guitar amp and after it's turned on it's silent for about 20 seconds, then starts making loud popping noises. This is with the volume all the way down and the cable unplugged. After about a minute of this it stops making the sound and behaves as expected. I've noticed that one of the two power amps flashes blue in time with the popping. Why does is this happening and is there anything I can do to fix it or should I just return it?