Im noticing a groaning/moaning noise coming from the rear of the vehicle when hitting anything above 45 mph. I purchased the vehicle from Florida in April of 2021 with 100k on the clock and I'm the second owner. So I'm unaware of the type of service its received prior to my ownership. The noise isn't a grinding sound and sometimes I'm so used to it that it sometimes makes me think its normal. Its definitely not the exhaust. A friend of mine tells me I should go get it checked out. Has anyone experienced anything like this on their W166 platform? I'm not sure if the diff or transfer case are the same between models.

Check the fluid level in the rear diff. If it’s a howling sound that changes with speed, then that’s where I would start. If it makes more noise around corners on the road then check the wheel bearings. I’m not too familiar with working on these yet but that’s the basics anyways.

Propshaft
Axle (differential)
Halfshafts
Wheel bearings

1. Diagnose at highway speed when it is making noise. Tip into and out of the throttle. If propshaft is not indicated (see below) this points to axle, wheel bearings or halfshafts.

2. Diagnose while accelerating at moderate torque from zero mph to 60mph. Note sound or vibration occurrence at specific speeds. This points to propshaft.

3. Diagnose at highway speed and swerving (carefully with no one around you) left and right. Do this several times. If the noise modulates while swerving, this points to wheel bearings or halfshafts.

4. If 2 and 3 do not affect the noise, this points to the axle.