I just got my new used amp home the other day, and now it started giving off a loud slamming pop sound, almost like a firecracker, when I turn it off on the on/off switch on the amp. It is quite loud even if I haven't turned the amp up very loud. It didn't do this when I first got it home, just started doing it today. The amp seems to otherwise work flawlessly, just worried that it might be a sign of a developing issue or that it will damage the speaker in the long run. What could cause this issue, and should I be worried?