Wow, this posting has had an unusual amount of replies. Here's my two
cents...

How is you home heated? How old is your house? How often and when do the
noises occur?

I've heard a variety of noises from heating systems caused by air in
baseboard heating radiators, air in the water pipes and air ducts expanding
& contracting. It also could be the house settling through the day.

No, I don't think barnyard animals are borrowing you car and you house isn't
haunted.

Handi_ca