I've noticed a slight noise at start up, not moving, still in park. It seems to be coming from the left front. Like when as kid we would blow gently into the top of coke bottle and it would make that subtle howling noice. I replaced the serpentine belt, tensioner, and idler pulley a few months back. My guess is the idler fully bearings could be faulty. But before I replace it, just checking to see if anyone else has had this problem and found it to be something different. It tends to eventually go away after driving.