Im getting a distinct and annoying buzz on a newly acquired 68 PR. It was something I was aware of during the sale, so it helped in the negotiating. The buzz is present once the volume gets over 4-5 and when hitting low notes. I have troubleshooted the following: - tubes replaced, still buzz - reverb tank removed, still buzz - baffle and speaker removed...no buzz! Nothing appears to be wrong with the speaker, but its vibrations are causing that buzz once screwed to the cabinet and baffle. Thoughts?