WTF is this noise?

[Freek]

I keep hearing a high pitched ringing noise that's going rrrRREEEERRRrrr and the pitch is going up and down. I can hear it all across the house. It's really quiet.

[Ad Bot]

[beachbum111111]

Go outside and see if it sounds like that there.

[sorrel]

Your house has invisible cicadas

[Freek]

Go outside and see if it sounds like that there.

Just did, it was an air conditioner.