I have strange noise at different times on my 1972 116 3.5 L, SLC.
Using a listening device I have be able to track it's strongest point of sound. I seems to come from the supplementary air valve. This sound comes whether cold or warm and doesn't do it all the time at all. A light grinding sound. Recent work done on car was timming chain, valve seals etc. The sound started after this work was performed. Car runs excellent, no problems at all. Sound is there whether in park or drive zones.

Anyone have any experience with the supp air valve and why there could be a grinding sound coming from it.

Thanks for any ideas.