My new Blues Deluxe occasionally will start to quietly hiss and create a sort of static sound, even with nothing plugged in. It happens on both channels and does not seem to affect the guitar sound, as far as I can tell. Also none of the amp's controls seem to have any effect on it. Sometimes it goes away on its own, sometimes bumping the cabinet will make it stop. I have tried wiggling and reseating the tubes with no difference. I have heard a lot of complaints about reliability with these Hot Rod series of amp and perhaps I am experiencing that. It is within my return window but I really don't want to have to return it if is something simple. Any ideas?