The other day I started up my 07 Mellow Yellow MCS and it sounded like the muffler was falling off up front. I lightly brought the revs up and the sound became louder. I got out of the car and looked under the hood. It sounded like it was coming from the top of the engine. After about a minute, it went away and I haven't heard it since. I checked out the complete exhaust system and everything feels tight. Anyone had this experience?

 

I had this happed the next morning after detailing my car. I parked it after washing it and in just moving it to the garage did not sound like that. The next morning it had that loud sound like what you described but went away after a couple minutes of driving. Got to work and let it sit the whole day and came back out and sounded normal when going home.

Not too sure what it could have been.

 

Me too. I have that rattling sound in morning sometimes, then a couple of minutes later it's gone.

Valves or lifters?

It's something that tightens up pretty fast as the engine warms up.

One morning it bugged me so I opened the hood and jumped out, went away too fast for me to locate the general area.

 

No matter what. I don't like it and I can't help but think it is just the beginning to some larger issue.