Strange noise from engine

[gfurm]

I have 2001 S60 D5. For last couple days I noticed strange noise coming from the engine. It can only be heard when on idle, adding just a little bit of throttle makes it go away. It sounds like an old diesel engine, not like D5, quite rough. But there's no vibrations or any other signs of something seriously wrong. No sign of it while driving, even very slowly.

What I noticed when looking around: the longest part of the timing belt (from big pulley on top going down, looking from front) is "flappping" a bit, and I think it should go in straight line. Like there's not enough tension (I can twist it more than 90 degrees). Can that cause this noise? If it's that is it dangerous?

Thanks in advance for any tips

Greg

[Happygilmore78]

Not saying it is, but i had a similar thing on a fiat i owned, and it ended up being a knackered pulley at bottom of one of the belts - that went away with revs, but was petrol - strange sound it was. Someone will no doubt know for definate on here

[Liddo]

If it is, best to get it do as soon as, before it goes altogether. Are you due a cambelt change???

[gfurm]

Cambelt, tensioner and idle pulley were all replaced at 96k miles. Right now it has 125k.

I'm going to a garege today so they can have a look at it and tell me what is it. Was told that from my description it may be alternator pulley.