On cold starts, basically anything below 60-F, there's a noise that sounds like a diesel engine idling.

2012 Boss 302 (Stock) with 23k miles...

It goes on for a while until (im guessing) the engine warms up to a specific temp. Once it hits that temperature, it shuts off, almost with a valve closing sort-of sound.

It does sound like its vibrating/rattling more as the RPMs rise too.

It's been at the dealer for a week now and they've been looking at all sorts of things (i'm told) without avail.
They're about to start looking into the engine.

I'm a little worried but only because its a used car and I'm afraid the previous owner may have done something warranty-voidable to the car and I'm stuck with the bill.
It looks all stock, sounds and drives stock.

So, I'm not crazy worried. I just don't know what kind of damage if any to the inside of the block would be noticeable and worth voiding a warranty...
Ex: Tune, driven hard, etc.

Thanks for any help!
I'm pretty good with figuring out car problems, but this one has me and, i'm told the service techs, stumped.

It's going back into surgery sometime today hopefully, so hopefully i'll find out more.

 

Maybe someone is interested in this weird issue... and if so! Here's the latest.

The dealer is telling me that they're thinking its a timing belt issue. They're waiting on a piece of equipment that will test the oil pressure in the engine. Then, they'll go from there.

However, I saw this posted on another thread by Gogoggansgo:

Could this be the issue?
Anyone with extensive knowledge would be an awesome help!

 

Final Update!

Apparently this is a normal sound that I did not know about. From Ford Engineering:
For the 2012 Boss 302, on cold starts, the forged pistons will make a rapping/clattering sound against the cylinder wall until expanded at normal operating temperature.

 

I don't think you should have to worry about if the car was driven hard it's a Boss that car is and was built to be at the track and driven hard everyday if you want. And I don't know why any other Boss owner didn't chime in on this and either agree or disagree with the resolution.

 

If you're reading this after reading all the other threads I've responded to, I'm sorry.
The final verdict was and is the starter. The sound was NOT the pistons... there was just no way.
It was a bad starter. The dealer replaced it and the sound is completely gone!
Thanks to all those who helped out!