When i first got the amp (new) about 2 months ago, i did notice that if i tapped the front of the amp where the knobs are,it sounded like i was tapping the tubes and they were about to go into self oscillation.Pretty much the classic sound of a microphonic tube.Was recording in the studio earlier and noticed some weird rattles coming in on certain notes on the E string.Pretty sure its a bad tube or 2.Just wondering if anyone else Royal makes a similar sound when they tap the front gently.Im gonna swap a few tubes out tomorrow anyway to be sure.Cheers