I received my new 990/7500 bundle last week and I've been listening extensively to it. So far so good except I do hear this ~1.5 sec chirp (high frequency hum/buzz) after power off (manual or trigger). It's not loud but definitely audible and worrying.

With some experimenting, I determined that this only occurs on the center channel when balanced input is selected (XLR cable connected or unconnected). I also tried connecting to a different speaker to make sure it wasn't crossovers doing it and confirmed this was independent of speakers connected. Having eliminated all possible external causes, this must be occurring within the 7500 and specific to the center channel balanced input.

I have submitted a support request ticket and waiting for a response but saw this thread and thought folks might be interested.