took a video of what it sounds like

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Tried using a mechanics stethoscope to identify where it was exactly coming from and no luck.
Any ideas as to what or where it is coming from?[/align][/align]

 

Almost sounds like an exhaust valve. Did you check the exhaust manifold (probably near the rear) for a leak?

 

https://mercedesforum.com/m_77684/tm.htm

I posted this and it may be helpful to your problem. I think the sound is OKish.