High pitch faint ringing noise

Zoolooter

My Bogner New Yorker head fell off it's 1x12 cab (with the help of my 2 year old), and now there is a faint high pitch ringing noise when a playing.

The amp sounds ok, as it should, apart from the ringing. All tubes seem to be glowing as normal. 2 x 6V6, 1 x 12AY7 v1 and 1x 12AT7 v2

Damaged pre amp tube maybe? if so, anyway of telling which one? 

olafgarten

Try swapping the V1 and V2 tubes and see if the sound changes. Look for any visible damage as well.

Actually, don't swap them, just realised they are different tubes. Just try reseating them, they might have come loose.

Maynehead

Sounds typical of a microphonic preamp tube to me.

Try tapping each one with a pencil while the amp is on. If one of them rings like a bell then you've found the culprit.