Fender Super Reverb (Reissue) Troubleshoot

[JDalton]

The following is a clip of my Super Reverb that I've had since 2007. The volume may be low, and I apologize for that, but you should be able to hear the problem I'm having just fine. As soon as the bass comes in, the sound is horribly compromised by way of crackling, buzzing, etc.

Sorry the music's not more entertaining... I was just trying to get the problem to be as audible as possible. You'll get the idea by 0:30 or so.

http://brianeltomi.com/Thisampsoundsbad.mp3

I've recently replaced the tubes, and I've already gone through the conventional methods of checking the tubes (e.g. tapping underneath, tapping on top of amp). They seem okay.

It's not the guitar, either. Sounds fine on my little champ 600.

I'm hoping to get some troubleshooting assistance from some more experienced musicians/amp experts.

Any help would be greatly appreciated. Thanks so much.

- Brian