Bizarre Problem...weird knock/tap/noise
 

Ok I replaced all five glow plugs to defeat my starting problem. This was a success.

I back the car out and after about 700 ft a tap tap tap sound is coming from either the engine bay or under the car. It coinsides with the speed of the engine.

However, when I manually rev the engine while it is in park from under the hood, the sound is not really pronounced, I cant even tell if it is there. I am going to pick my indy's brain tommorow, but I hope its not engine trouble. The car has been running perfect and I have never had any engine related issues.

Any comments?

I have this same issue. I have not isolated it as of yet. It seems to happen more frequently when the temperature is colder.. and I've heard it both in the morning when first driving the car at low speeds and at night when on the highway.

Is it the muffler/tail pipe rattling against the body? Mine some times does it at idle but goes away when moving. I need to replace some rubber hangers.

Feel or listen for nailing at inj fuel lines; then look at flex disks.

Any chance it's chain slapping? If it was me I'd probly replace the tensioner (cheap less than $80 part) as regular maintenance at 190k miles. And good news is MB used alloy metal chain guides that never need replacement back then. So if ye ever replace the chain on pre-78 MB, then NEVER let anybody replace old metal guides with crummy new self-destructable plastic ones.

I am having the EXACT same problem with my car. It makes a taptaptaptaptaptap when doing anything in drive, and if I free-rev in neutral, it'll start to make the noise around what I guess is 2000-2500 RPMs as well.

I'm getting ready to do my fuel injectors (ordering the injector socket, bought myself a torque wrench, etc.) and hope that helps...if not, I'll probably have to have my indie replace the timing chain and associated components.

Injector? Lifter?

Kyle try cracking the lines one by one and see if it goes away.

Ditto on that hatteras. How loud is it? Might also just be knocked off carbon, be careful as this can damage the PC and cause many worse things to happen.