Tube mic making horrible noise

...before I start using it!
 
Hi guys,
 
I have an Alesis tube mic (re-badged GT). It has worked great every time I get it out of the box UNTIL this morning when I start to work through the remaining tracking for an album project (working with a deadline as I've booked the mastering session).
 
I plug it in and it's registering an inconsistent but highly noticable background noise (not unlike white noise) up to around -35. Highly unusual. I try to replace any of the parts of the power and signal flow chains to iliminate the offending link but get no joy. The mic doesn't get used everty month and last time out it was fine.
 
Any ideas? I'm back to using a small diaphram condenser on acoustic guitar which is ok but I have five tracks of lead vocals to do, too :-(
 
Any help greatly appreciated, as always.
 
Dave

Hi Mike,
 
Thanks for your help. It's a glass tube. I took the casing off the mic to see if there was anything obviously out of place (to my untrained eye) - I didn't see anything. The tube and socket looked pretty clean, too.
 
I'll try your suggestions - thanks again.
 
Dave

If you do need a new tube, I may have one for you if it's in the 12AT7 or 12AX7 variety.

Sorry for the shameless plug, but I bought a **** ton of tubes to try out, and have a bunch of good vintage tubes that are for mics and rack gear.

http://stores.ebay.com/Fogelsang-Studio?_rdc=1

I have more problems with new production tubes than cars have pills. So I stick with the vintage stuff. My knee jerk reaction to new tube gear is pull the tubes and replace them with the 50's and 60's stuff (most times before I even power them up!)