i've actually had this same problem. just bought airpods pro a week ago, put them on for the first time and this high pitched ringing sound started developing (i guess tinnitus). i hear it without the airpods pro on, and when i think it's almost gone, it gets refreshed whenever i put the airpods back on, thinking the noise wouldn't come back but it always does.
i was on the verge of returning them, but wanted to do more research. i searched this problem some more and found this other thread. i tried again, this time shoving them in my ear and making sure it's sealed, and voila, the high pitch noise is gone. granted, the tinnitus is still there from the first times i've used them (and i hope it becomes milder), but i guess i found the source of the issue.
for those of you getting a high pitch sound, make sure that the earphones are sealed when you wear them.
for those of you who don't experience the high pitch noise and want to, try wearing the airpods pro like normal earphones (hanging in your ear, not stuffed in, like normal earphones), and enjoy some high pitched ringing (warning: may cause/trigger tinnitus).
btw these experiences have all been with noise cancelling on. the other modes, transparent and off, have been fine, if not better.
as for me, i'm going to return these. as much as i want to keep them, they're too inconvenient to have to shove into my ear, or risk refreshing tinnitus (tough tradeoff lol)