What's the Frequency?

[JustMike]

 When the OP primaries are incorrect, a high pitched squeal is heard (by some). What is this a product of? And can the frequency be calculated? The reason I ask is that when I put a new OT in my build, I took the amp upstairs to my music loft to test it. I turned the amp on and while I was waiting for it to warm up my wife yells from downstairs about 30 ft away- "Gawd, what is the sound?". I heard nothing. I know I've got hearing loss, but this was a little shocking that I heard nothing.
 I swapped the secondary leads and she hasn't said anything since.

[shooter]

I believe it can be any, or all frequencies
it happens in amps with NFB, but it's actually positive feedback because of phase, so the amp "runs away"


I'm stone cold deaf above ~~12k, did the same kinda thing "spec'in" a stereo, i'm happy as a clam looing at waveforms on a scope I don't hear, Pam n the cats are going ape sheet 
I build a dummy load 

[Joel]

You just described my wife and I....  and my daughters and I.  Most high pitched sound is either masked by my tinnitus or I can't hear it.  Then again, my girls are deaf in the frequency range where my voice sits...

[Williamblake]

If you have a smartphone you could download a wave generator app to test what you can hear. I use "frequency generator" for android.