when I start my car for the first time in the morning, there is a loud rattling sound that comes from the engine compartment. It sounds like it is on the passenger side of the engine. When the car is warm and I shut it off and turn it back on. It will not do that sound only when it’s been sitting overnight, it only rattles for about one second I cannot find anything loose in the engine compartment but it sounds metallic in nature. Any idea what this could be? I bought the car with 400 miles on it and now I have 115,000.

 

Honda Service Bulletin 16-088 (do a Google search)
Engine Rattles at Cold Startup
VTC Actuator must be replaced.

Numerous threads about this problem on this site.