EDITED - NOW WITH NEW / MORE INFO! I know this is a Guitar Cab question, but I put it in Misc and was told to move it here so... Today when I plugged into my Marshall 4x12 guitar cab is made a horrible buzzing mweeerrrrp sound when I played. It sounded like the entire cab was vibrating. Very bad. It only happened when I played with a bassier distortion and was much worse on certain notes / chords, notably A#. I wasn't pushing the amp too hard (reasonable volume) and was running the correct ohms from amp to cab. A friend said that the cab might be 'tuned' to a certain frequency and that the cab was sympathetically vibrating when I played near or at that frequency, but that seems a bit crazy to me. Then I read a related? thread here on TB - could this be from underpowering? The head is a SOVTEK MIG 50: 50 watts (selectable ohms - set to 8) and the cab is the MARSHALL 1960B STRAIGHT: rated 300 MONO / 150 STEREO and I'm running it mono (just using one input, set to mono | selectable ohms - using one input also set to 8). The underpowering thread went WAY over my head, and was geared towards bass amps (where clipping is an unexpected and generally unwanted phenomenom). How close do you need to be in terms of power? Am I underpowering the cab? How is this all affected by using distortion (clipping)? How is this affected by class A or class A/B? I am very confused! HELP! Any ideas? Anyone know where else on the net to ask? Who can help in this hour of distress? Thanks in advance!