Mine is about 9k-10k I think .. mostly on regen coasting/breaking <40mphI get that too - very high pitched (maybe 12,000 Hz) but not higher. Kids can hear higher Hz levels than older folks.
This and Bluetooth static are on volt case# 71-128754793. My daughter and I can hear it .. my wife can't (and she's the one always asking me if I'm deaf!) LOL