Benz 2003 e 500 groaning noise

2003 mercedes benz E 500, 138000 miles v8.
I hear a groaning noise just after take off on my 2003 E 500 mbenz. I think it is the suspension raising the car because when I manually raise the car while parked it doesnt make any sound but when driving it makes similar sound as when the car is apparently doing it by itself.
I just tried that as a test. Im not sure if the car is supposed to be adjusting its height by itself while im driving. But I constantly hear an annoying load groaning sound for about 10 sometime 15 seconds then it stops then comes on again. It happens mostly at low speed also upto 40 mph.

Does anyone know whats going on and how it can be fixed?