I took my G35 to my mechanic to replace the valve covers and spark plugs last week, and ever since then a rattling has occurred from the engine compartment when I travel over uneasy or pitted pavement. It sounds like its coming from the top and center of the engine - any idea what could be causing it? I've thought checking the engine cover, but this seems elementary. Is this related to the work done on it at all? Is there something I can tighten or torque down? Thanks in advance.

 

I say just open up the hood and start pushing on things to find out what's loose. Sounds like the mechanic didn't re-tighten something.

 

maybe he left a tool under the hood.. i've seen that happen before