One morning my `91 300 D Turbo (290K Km / 180 K miles) suddenly developed a terrible rattling noise on idle. The rattling disappears completely if the rpm are raised to about 1000 and appear again on idle after that. It's sounds like the noise come from the front side of the engine. My guess was that it is the timing chain. However, I thing the chain starts to make noise more gradually, not from one day to the next. Therefore I thought that may be the timing chain tensioner was broken and I replaced with a new one, filled with oil as it was described in the manual. However, nothing changes.
Could it be that the sound comes not from the chain but something else or I should go directly for a new chain?
Thanks.