This is going to be a little hard to explain. My '05 MCc has developed a noise that I am trying to identify. It happens when I start the car in the morning. It sounds like something is hitting. Metal on metal. If I immediately shut the car down and start it again, the noise is no longer there. I believe this is a recent development, less than a month. I did not hear this when it was warmer, although I am not sure weather has anything to do with it. It also does not do it at the end of the day, even though the car has been sitting in the garage for 9+ hours at work and is completely cooled down.

So, does anyone have any ideas?

 

Location of noise?

 

Exhaust hangers broken? Heatsheald loose?

 

The noise is coming from around the left hand (driver's) side in the vicinity of a firewall. What's puzzling is that it only happens in the morning when I start the car. As said above, if I shut the car off right away and start it again, the noise does not happen.

 

Do you hear it with the key in run position, but not cranked? or only with engine running?

 

It happens when I start the car. On the first crank. Single noise that sounds like a metal bar hitting a metal pipe. <BANG>. Does not get repeated till next morning.

 

OK, just some possibilities off the top of my head: check the belt tensioner for smooth operation, and check to see that the exhaust hangers are not letting things move around too much. I know these aren't in the left firewall area, but sounds can get transmitted in different ways.
Best bet is to have someone looking under-bonnet when you crank the car.
Also, if a motor mount is broken, you could get some excessive movement of the engine, allowing things to bump which normally wouldn't.
Good luck.

 

Did you check the passenger side upper engine mount for leaks?

 

Yes I did. Does not look like it is leaking, but I will be putting in some urethane bushings next week.