Am I hearing things?

Agree with mickeyb

I had a licensed electrician install a 20 amp circuit for a 4bSST2  (thinking I might later run a pair of 7 monos.) It has the 20 amp circuit breaker. The remainder of the system runs via a 15 amp circuit. No problem

My home is 100% electric, and the major sources of use are the cooktop, water heater and dual  heat pumps/air handlers.

+1 @mickeyb 

Do not put a 30 Amp breaker on 20 amp wiring/outlet. This is life endangering, not to mention illegal. 

Of all possible tweaks, don't do this one. 

Actually you should swap out the 30A breaker for a 20A breaker and leave the outlet alone.

You obviously don’t know a thing about AC. 

If you forced the wrong BRAND breaker into your box, you could be in for a hot time. You know, (unlikely) what I mean, right?

Some breaker brands will “fit” into a different brand of box. But the contact may not be good so you may get a lot of resistance and heat build up and this can cause an “electrical fire”. I don’t have the patience to explain this to you, but if you think you may have made this mistake you have made a dangerous error.

The 30 fuse in a 20 circuit is just plain dumb, but it will not, by itself, cause dhrillness .< that IS a period. There is an easy cure for your shrillness - wait two weeks.  You will be acclimated to the “new sound” then and you will probably put it down to “burn in” - unless your house “burns down” first.

Hiring an electrician is quite easy. Learning how to BE an electrician is much more difficult.

”Burn in” is an audiophile mental construct. “Burn down”, in your case, may turn out to be an audiophile physical “destruct”!

Good luck.