rumbling at idle

Hi there, first poster here to pardon me if I'm posting in the wrong place. It's giving my head in because I don't know what this is. Whenever i start the car after leaving for 2-3 days, there's this rumbling sound at idle, and when put into Drive/Reverse, it will produce a thumping sound at...

Hi. I have a c180 2004. The problem is when I put it into drive or reverse there is a rumbling noise coming from the front somewhere. It stops when I pull away. Someone suggested it could be something to to do with the belt tensioner/dampener?? Thanks for any light you may be able to throw on this.