The Sound of Tubes Going Bad?

Does this sound like the sound of tubes going bad?

Got home tonight and powered up the stereo. (Separate power amp and preamp, both tube.) Last listened to it two nights ago. There was a loud, constant cracking noise coming out of the speakers... and when I disengage and engage the mute, I get a loud thump/pop out of the speakers. After 1/2hr warm up, the cracking sound went away.

My amp auto-biases. Amp and Preamp are 5 mo's old. Amp has 4 KT88/6550s, 4 12AU7, and 2 12AX7 tubes. Preamp has 2 12AU7 and 4 6DJ8/6922 tubes.

Thanks for your observation.
Yes, probably. If it depended on the mute then I would look to your preamp.
try to dust off the preamp volume control.It probaly fix the problem.Nothing wrong with your Mute swicth.Good luck
The crackling sound sounds like small tubes in the amp. If it crackles after you engage mute it is. If it doesn't then its in the preamp. Since its in both channels I'd replace the small tubes in the offending device. That might well also correct the thumping sound which I believe may be caused by a DC offset.
I have to say this. In the future, Do Not Turn Off Your Equipment. EVER. Everything lasts soooooo much longer. The components and it's internal parts (as in resistors, capacitors, ... and yes, even Tubes) all last forever if you don't have the constant demand of expansion (heating-up) and compression (cooling down) straining them. A piece of equipment left on for years will always outlast the same piece that has been turned off and on.

I learned this in a very professional recording studio I engineered at for 5 years. Nothing was ever turned off there. We had Very few equipment problems. (Mostly mikes beaten by crappy drummers).