Yes, check the rear self-leveling suspension (consisting of hydraulic struts, accumulator cells, leveling valve, and hydraulic fluid circulating through a pump part of the power steering pump to the valve and accumulators, and back to the reservoir in the driver's side front engine compartment). Is there hydraulic fluid in the reservoir? When was it last changed? Have the accumulators been replaced ever (they wear out like shock absorbers)? Now, use the search function above, search "SLS" or "self level suspension" and you will find a ton of information. This is a common issue with our TEs.