Returning Noise in a Fender Hot Rod Deluxe

[TerryD]

My friends amp was making a terrible noise like only when he played a C in just about any position.  I tightened the tube sockets up real good, I think...It played great for a while and now that noise is back with a vengeance.  Only on that note.  I know this kind of noise comes from a loose something, but I perplexed that it would go away and come back.


Any ideas?
Thanks,
Terry

[PRR]

Low C *and* high C?

Tried another speaker? (A speaker is more likely to very narrow-tuned troubles.)

[TerryD]

I'll check it.

[TerryD]

Interesting.  It was the speaker, but not the voice coil or anything.  One of the stupid chassis screws was pretty loose and another was a little loose.