My car has been at the dealership for the past few days due to rough idle, loud metallic ticking sound from the engine, a check engine light on, and a whining noise coming from the differential.

The service department has decided that the differential needs replacement. I am wondering is there a break in period for the new OEM diff? Should I observe the 600 mile break in like when the car was new?

Also, they are telling me that the metallic tapping sound was caused by a bad plug/coil. Is this possible? I find it hard to believe that an electrical item with no moving parts can make a metallic tapping sound. They say the rough idle was caused by the same problem, and that the computer was reporting misfiring. This makes sense to me, a bad coil/plug probably would cause rough idle and the computer picked up on it too. Why would a plug go bad in only 28K miles though?

Does Anyone know if a coil/plug can actually make a tapping sound? It really sounded like a valve out of adjustment or something of that nature. I have a friend who has access to a boroscope, maybe we'll take a look down the cylinders just to see if we can see anything bad going on in there.

 

A spark arcing can sound like a tap.

 

How long did the differential replacement take? Any idea why the original failed? I'm scheduled for a differential replacement since mine is whining. The diff also has a leak.

 

I hate to say it, but if it sounds like a valve out of adjustment you should pull the #4 spark plug and check it against the others. You might also see if the dealership has a bore-o-scope to look at the cylinder walls in #4.

Just to be safe....