Need some help, Im not sure if our ML has some issues. Its 2014 BT with 53K on the clock.

When accelerating fast I'm hearing the engine noise/knocking very similar to a gas cars when running on low octane gas, as soon I release gas pedal knocking goes away.
If accelerating slowly engine sounds normal.
Im not sure if this sound was there all the time, hard to tell but its bugging me now.
I did try Shell, Chevron and Safeway diesels, no difference.
Any ideas? Should I just crank up the music and forget about?

 

We have a 2014 with 50k miles on it - while it's my wife's DD, I believe I have heard the same noise you're referring to when accelerating, which I believe is normal "diesel clatter":

http://mechanics.stackexchange.com/q...-clatter-noise

But having said that, I don't notice the same in my DD, an A6 TDI...