I get that too. It sounds like a servo or pump. Does the sound you hear come on for like 3 seconds and then click off?

The TCH has some additional hardware that makes different sounds. After I park my car, I can sometimes hear my car doing things up to 20 seconds later as well. I haven't done any research on these sounds, but they sound very normal to me (no grinding or scary noises). I think the vehicle does "maintenance" or calibration on itself after each trip.