Rebel 20 Noise help

Hey, there!

I bought a used Rebel 20 in great conditions and have been using it extensively for the last couple years without problems. Recently, it started whistling and crackling, took it to a tech who told me it was the preamps tubes going south. Changed those for Mullards and the amp sounds great, BUT it started having this noise, almost like the bad tube crackling, but more like interference, as if the amp has become highly sensitive...

The only other thing the tech did was biasing the amp hotter. At his shop, with a regulated ac and all the bells and whilstles, the amp doesn't act up, but everywhere else, the noise is there. Does biasing therebel 20 hotter makes it more prone to noises and interference? I'm going nuts and I really depend on this amp to gig, I thought I'd give this forum a shot.

Thanks!

Bias level shouldn't impact noise pickup. The tube sockets might be dirty or have bad solder joints.

..or the preamp tube microphonic.

hmmmmmmm, the plot thickens... Brand new preamp tubes. Thanks, I'll give those a try

Still likely a tube. Even a new one can be bad.
Does it do this with the master volume all the way off?

Wow! Mr Egnater, yes it does. Thank you very much for your reply, love my amp!