new speaker whistle

[Road King]

Fender Hot Rod Deluxe - just replaced OEM tubes with SED C wing 6l6GC biased at 68 and replaced OEM speaker with V30 Celestion. Turned amp back on to find it whistling. NO guitar plugged in or anything. Any ideas. Got a gig in tomorrow. Kinda freakin.

[Road King]

It appears that v3 went microphonic and the whistle is gone with a new tube. I have lost some volume though and gained some hum and buzz.
Any ideas?

[olddawg]

Put the old tube set back in and replace them one at a time. Could be a bad or mismatched tube. You didn't reverse the speaker leads per chance? Why do you prefer Celestian over Eminence for a Fender?