Here's a confusing one... '85 300d NT.

Clicking noise emanates from the engine compartment when driving car under medium loads/speeds. It occurs in both forward and reverse. Strangely, if I drive the car lightly or at high loads the noise is not present (or extremely rare); it likes only marginal throttle and about 40-55 mph. Clicking noise is irregular and sounds very sharply (like breaking a stick) almost without pattern. Frequency of the noise can best be described as two nuts being disturbed irregularly in a tin can.

Noise occurs irrespective or road conditions, temperature, etc. It occurs one or two times in reverse if I punch it then back off. More commonly, it occurs in drive when going on straight-aways (country roads) at 40-55 mph when I'm NOT accelerating or decelerating, just maintaining speeds on flat runs. If I accelerate the throttle further the car will drive to higher speeds and maintain them without the noise reoccurring. Noise does not occur in neutral when revving he engine.

I inspected the engine compartment and could not find anything obvious. Checked air cleaner mounts and most of the frame mounted accessories. Could it be the engine mounts, the fan hitting the shroud or a belt driven accessory? Could it be an internal engine noise? Could an old exhaust cause this noise?

This noise has not “suddenly” occurred; it has developed and become more frequent. Any thoughts?

Thanks,

ATLD.