Hello y'all and Happy Christmas! I bought a 2006 Ampeg SVT410HLF a year ago and I've used it with a V4BH from 2003 since then, with a BATW Revelation SuperBass Preamp/OD/Dist pedal infront. In the last few months I've been driving myself insane trying to figure out why when the treble is turned up or when I turn up the tweeter there's a certain note (A#) that hizzes, buzzes and crackles. The amp does not stop working, it just adds that disgusting sound that become louder and louder as I turn up Treble freq. and when I roll up the tweeter on the cabinet. I've learned now that distortion can harm the tweeter, but if I turn the tweeter completely off I can still hear (although much, much less) that disgusting sound. What more is, when I put the head on another cabinet while still plugging into the 410 (physically separating the two) the disgusting sound dissapears almost 99%. It leads me to think that either: 1) There's a loose component somewhere that rattles and causes the sound, but that doesn't explain why the treble makes it louder when the more obvious would have been the bass freq and it wouldn't be just the one note, A#. 2) The tweeter is broken! But wouldn't it be completely out of the circuit if the tweeter control is turned off? The one on the back of the cabinet. 3) There most be something else wrong or a combination of the two. The two techs I've sent it two couldn't figure out the problem. I've tried all sort of cables and combinations, and I tried another head on the cabinet that didn't cause it to rattle althought that head blew after 30 minutes because it was old and very sh*tty... So I couldn't compare more after that. I've connected guitar heads to the cab without problems and I've played the guitar through it with no problems. Please, somebody here who's an experienced Ampeg gear user (and abuser) please help me out! I'm a guitar player, so it's really just my gear but my bass players borrows it and it's driving me nuts that I can't figure it out and I hate spending cash on something that I can't fix.