Odd noise at 30 MPH

[Trickythemerc]

I am getting a strange sort of rumble type noise at 30 MPH almost feels like its in too high a gear and the engine is labouring. Above and below 30 it is fine and if I knock it down a gear it stops. I am going to have a gearbox service done anyway as its on 74k with nothing in the history about it being done.

Any ideas or clues please

 

[BlackC55]

What car is it?

It could be a torque converter judder.

 

[Trickythemerc]

ClK 220 CDI 5 Speed Auto 2009

 

[BlackC55]

Go on a road test with a Merc tech and get it plugged in. A specialist or dealer is your best bet.