power steering pump noise when turning
Check the fluid level, if full then it is most likely a pump getting ready to go. You can try flushing the system and see if that helps, but if it is really whining then it's only a matter of time.
Tennisshoes is probably correct. But at 13 yrs old this would not be an unusual repair. Waiting on an MB repair usually guarantees a higher cost because so many things are inter-connected.
Looking for a Used M-Class in your area?
CarGurus has 5,638 nationwide M-Class listings starting at $1,500.
Search Mercedes-Benz M-Class Questions
Mercedes-Benz M-Class Experts