When I start my 500E after it has been sitting a while (generally at least 2 days), upon start-up, I hear a loud, high-pitched squeal coming from the very front of the car. It lasts about 5-15 seconds and then stops. Sometimes, it sounds almost like tires squealing against a very smooth floor, but it's definitely not the tires.

Any ideas? Thanks in advance.

Frank
1992 500E
143k miles