It runs on AC but is controlled by 12v. Check your thermostat and make sure it isn’t on fan or cool.
First off, it’s incredibly filthy and disgusting and needs to be cleaned.
As u/cheeseman316 said there’s also 12v going to the unit from the thermostat. Turning it off should stop that sound.
Source: Can y’all hear the clicking sound coming from the AC? We don’t use it and have the breaker off for it. Any ideas how to make sure to power is running to it? It’s making the sound a lot now. Started today.