Hey guys, sorry if this has been posted before, I couldn't find any answers when I searched. I have a late 90's angled 4x12 recto cab I'm having issues with. I've been getting a nasty sounding vibration, particularly with notes in the lower register ( picture the noise a light saber makes when its turned on, but louder). For the life of me, I cant tell which speaker its coming from, and all four speakers appear to be intact and not blown. Ive tried ot through a couple of amps and its the same with both. Any ideas on what it might be? I'm pretty solidly stumped...