Hi, I am new to the site so please bear with me. I have done a search and cannot find my exact problem. Some back story, I have a 79 240D I picked it up about a year ago and have really only put about 2000 miles on it, and 1800 of those were a long road trip last fall, as soon as got it I took it to a benz only shop that is highly reputable and had the fluids changed, the valves adjusted, and whatever else needed to be fixed fixed eg, neutral safety switch, glow plug relay, starter, this car sat around for years not being driven much.

Here is my problem, since I owned it it would tick under light acceleration intermittently normally right before shifting tick tick tick shift, then repeat for the next gear, its a auto, drove about 1600 miles then I noticed the same intermittent ticking would happen at a constant rpm/speed around 45mph if I hold that speed I can get it to tick more rapidly and it will sound like pinging from a gas motor. I have not really driven it in about 6 months because I don’t want to do any damage. The car is quite and idles good, drives great, and under heavy load and acceleration there is no ticking at all, I can make it happen by revving while parked but not consistently. the noise sounds from inside like it is down lower on the back of the motor, standing outside revving it is hard to pin down where the sound is coming from?

any thoughts?