I'm not quite sure why, but last night at rehearsal, using settings I've been using for quite a while, with the same guitar, I noticed a lower frequency "woofiness", particularly on the B note (G string 4th fret) when playing a G major - and to a lesser extent around that note. At home this morning I tightened every screw on the cabinet. Tested. Same thing. I reduced the bass setting. Fixed, but not the tone I want. I stuffed a pillow into the cabinet. Fixed it. So, it's clearly a particular frequency thing. Any thoughts?