I posted this over at the Boogie board and didn't get a response, so I thought I'd try here.
I have two different amps I use, a Mesa 50/50 and a Mesa 2:90. Both sound absolutely amazing through my good ol' Mesa 4x12 recto cab.
When the tubes are new in the power amps, the cab has all the low-end in the world and sounds like God. Here's the weird thing though. If my tubes are worn, the back of the cab rattles fiercely when I crank up the amp. So much so that I have to turn off Deep mode on the 2:90.
I've thought it was a problem with the screws being loose in the cab, but no they're all tight. I had my other guitarist play the guitar and I put my hand on the back of the cab, and it just vibrates fiercely and has this awful sound of the back plate vibrating against the wood it's attached to.
I rehearse with my band about 3 times a week at a loud volume, I practice at home about twice a week at lower volume, and I play 2-4 shows a month. My amps get a lot of use, basically. I also play 7-string guitar mainly and I've got a fairly balanced sound.
The amp still sounds great even with the worn tubes, they're only 6 months old. I don't want to replace the tubes every 6 months, because other than the rattle, the amp still sounds godly.
Also, it's only my cab. If I play my other guitarist's Marshall 1960 cab, no problem. I think when the tubes get worn a little, my amp just begins pushing a certain frequency the back of the cab just can't handle.
I'm wondering if any of you have had any issues like this and what you did to fix it, other than just replace the tubes
Maybe install a thin gasket of high-density foam (weatherstripping material) on all the edges and contact points where the back attaches to the cab, then screw the back on. This will probably also improve how air-tight the cab is.