Tube pre picking up feedback/vibration?

Still not happy with the results of the new tubes. Emailed ARC and they basically said all is well. Now I notice a low hum from one channel and reversing the wires leads me to suspect the tubed. What exactly will a bad tube sound like? Hear the hum with volume all the way down and the cd player stopped. Like I said I reversed the wires to the amp an
d the problem followed the change so I have ruled out the amp. Ideas?

Thanks . Will try to get this done today. Yes, retubed. Thank you spell checker!!
Tubes were purchased for ARC, 2 weeks ago, and I assumed they would check for defects before they were sent out. Go figure!
Again, thanks for the advice.

Thanks...great suggestions . I'll try to get time and let you know what I find.

Finally dug up an old set of Sovtek tubes, probably from many years ago, that were in a box in the basement. Put them in and took out the new ones ARC had sent me ...and no more noise, microphones, whatsoever!
To say I'm disappointed that they would sell crap like this is an understatement. These tubes are marked by them for the specific spot on the circuit board, but I guess no one actually tests them for micro phonics. Do they need to actually be installed in a preamp for thai to show up?? I figured one of the reasons that I should buy from the source, so to speak, was that they would send me something that wasn't a crap shoot.
Makes me wonder if I should look at this brand when I upgrade.
Anyway, problem solved. Now to get a replacement set that only make music when the signal says to!!..))