It has this tapping rapping not quite a knock sound, except when you're starting it, it's sounds terrible when it's being cranked. Then after it starts it runs fine except for the tapping, it's louder than just a tick tick like a tappet, but it's not a real heavy metal to metal thunk thunk either, except when cranking to start.
The thing about it is, if the engine is under a load, accelerating or if you brake and run the engine up over 1.1k or 1.2k, the noise just goes away, or at least is almost undetectable. It is noticable at idle, louder when decelerating, and loudest when cranking to start.
I've had it to the MB Master Tech. Had the bottom end checked, put in new rod bearings. Didn't help. Everything else looked fine. Compression test and leak down were good. Had the oil analyzed for metal particles, it seemed fine. It doesn't miss or anything. It doesn't use much oil or water, a little but nothing out of the ordinary for a 14 year old car. It runs fine, except the noise.
To me it sounds like it's right in the middle of the engine at cylinder # 3, but I'm no tech.
This thing has people stumped all over the east coast, and no one wants to say for sure what it is. Of course they won't mind charging to take the engine apart and start replacing things until they get it right, but I'd like someone to know for sure what it is BEFORE they start into it.
Any thoughts on this ???
Thx