2001 - S500

This week I got a "Active Body Control - Drive Carefully" message. After restarting the car the message disappeared, but now I have this noise coming from the front side of the car. It sounds like a moaning noise (hard to describe). There is no leakage under the car and the car has not dropped. The message has never reappeared only the noise remains. Could it be the Hydraulic pump? (Is it called a Hydraulic pump or ABC pump or Power Steering Pump). Is there anywhere I can check the fluid or add fluid? Reset something?

Last thing right before I got the error message I had the right side (front and back tires) of the car parked on a small curb because of a narrow street. Could this have anything to do with this problem?

Thanks