Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Any idea what might cause this unwanted 'halo' of noise mixed in with clean tones? Dry capacitors? Thanks for an help!

Also watching the Carlsboro thread below this thread, looks like it's a similar issue

It does! I'll watch your thread too :D

Most likely crossover distortion which sounds a bit like a torn speaker buzzing as the note dies away.
Easiest way to establish Xover distortion without a scope is to use the clean channel,,turn volume up about 1/4 way then just pick *One string Only* on your guitar and let it sustain normally as it fades you will hear a buzz like torn paper sound after the note.

You may have to put your ear close to the speaker if it's minor but if Xover is bad it's really obvious.
Bias can change over long periods of time as components can drift in value and hence Xover dist creeps into the sound.  Just replacing transistors in an output stage can alter the bias point and so it's wise to re test the bias.
Phil.

So does a rubbing voice coil.  Try playing the amp through a different speaker cab.