I have a 2007 Acura TL. On the first drive after have been sitting overnight, my car has a very loud rattling sound coming from somewhere under the hood, (not windows or glove compartment) in front of the passenger seat. The rattling sound gets louder and more rapid when accelerating. The rattle goes away if I take my foot of the gas. The rattle also goes away after a few minutes of driving. The longer I drive and more the car warms up, the more time it will take before a rattle will occur again. This makes the issue challenging to diagnose. If I drive to a mechanic, the rattle will no longer be occurring by the time I get there, nor will a be able to reproduce the issue.

Does any one have ideas about what might be causing the rattle? Or would I can do to better diagnose the issue?

 

A leaky timing belt tensioner will do what you're describing. Its also a common problem

Youtube "Honda J series timing belt tensioner rattle noise" or something to see if the noise and condition is what you're seeing.

If needed, buy the replacement from a Honda/Acura dealer. Like curryacuraparts.com

 

Yup, it probably needs tensioner. My Wifes MDX is also rattling on the timing belt side. Time to do maintenance there.

 

I usually go to Rockauto.com for genuine aisin/Gates timing belt kits. Best prices and fast shipping