1980 240d making pinging rattling noise

[Rick H]

hello i`m hoping someone may be able to help me with this problem. i`ve done a search and didn`t find anyone with the same problem. my car is making a pinging noise at high rpm`s almost like a gas preignition sound. it seams to go a way when the car is warm sometimes it won`t make the noise at all. it always makes the noise if the car has been sitting over night. i adjusted the valves but it`s still there. i tried cracking the line to each injector one at a time to isolate it to one cylinder but it didn`t seam to make a difference. any idea`s would be greatly appreciated thank`s