rattling front pully....??? 500SEL

[Twin Pipe]

my mates 1984sel emmits an erratic rattling noise from the fan belt area,does anyone have any ideas what it could be,we were told it could be the crank pully coming loose,is this possible.?? all the ancilleries seem to be ok.

[BrianDrought]

Should just be the belt tensioner. They do tend to go after a while. Quite cheap to replace though.