it could be anything, from the axles to an engine with a lack of oil.
I have a 2004 c230 and I had a squeaking noise when the engine first started. It was my water pump with uneven wear on the water pump pulley that was causing the sound. I will tell you it could be many different things, but this was my reason.
squeaking noise coming from sleeve covered arm coming from steering column to the wheel
loose belts
Your Axle
Most people will tap the brakes of a car when their car is going downhill, usually to keep the car under the speed limit. The squeaking noise could be the brake rotors or the brake pads.Ê
Loose belts
One of your belts may be loose or in need of belt dressing.
probably the fan belt
When you hit the bump, the mouse wakes up.
If you are reffering to tires, the wheels spin faster than the car moves so the tires make a loud squeaking noise.
maybe the axles need to be check
Power steering belt?