My car sounded like it had a tin can banging around under the hood shortly after I got it, then the water pump started weeping, so I replaced it (original I believe, it had 214k on it! ) and the can sound was gone! Just an idea, and thats at the front of the engine but sometimes where the sound is coming from is deceiving.....

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)