So have a 2011 MCS with about 15k miles on it. Went in for 1yr state inspection and a oil leak was found at the chain tensioner/camshaft. (had no idea even while running oil pressure and temperature gauges so who knows).

Dealership ended up "removing chain tensioner and installed updated oring" as it notes on the invoice. Since then, and now that it is getting cooler here in New England I have experience the issue found in the video below. On cold start in the morning and for about the first 5-10 minutes of driving I experience a "thick" rattle noise towards the top of a gear mainly 2-3000 RPMs. After about 5 minutes it goes away and then engine sounds normal again. The noise does NOT happen at idle, only at 2-3000 rpm and I believe only under load (i.e. not when revving the engine while parked)

Check out the video below. I am going to try and get a better one again soon.

After about the 14 second mark, towards the top of the gear (before slowing down) at about 24mph on the speedometer you can hear it best.



Also found this video below after uploading mine, identical sound but can't find any other information about it.



Of course, something that I can't reproduce for the dealer.

When trying to explain it to a different dealer, they mentioned possible drone from the wastegate opening to quickly heat up the catilitic converter. Never really understanding the drone sound very well means I dont know for sure.

I have searched around the "death rattle" threads and cold start issue threads I can not find anything like this at all. It does not happen when the engine is warm or at idle.

So are we thinking bad chain tensioner install/reinstall? I am worried I am causing more damage and can't get a loaner from the dealership since I am under 25y.o. and the issue only happens on cold start.

Any help greatly appreciated.

 

Maybe with the new O ring the tensioner now travels out less distance and so the chain is more loose. Did they also replace the tensioner with the new part number that applies more pressure and travels out more? That's all I can think of ...

 

I don't know... If it's that 'buzzing' noise (heard later in the second video; couldn't distinguish any odd noises in your video), I don't think that's from the engine compartment. Sounds like some kind of harmonic resonance in the cabin (or perhaps the exhaust) to me...

Check for loose bits in the interior trim, dashboard components, and maybe even the exhaust mounts.