Vibration from front of engine

[sbloxxy]

As the title says, I've got a vibration on my 2000 Boxster S. At first I though it was one of the exhaust heat shields making a racket again and I had a good look under the car and was surprised when all was ok. Its really difficult to pin point the source of the sound but eventually, after removing the front engine cover (behind the seats) it seems as though the sound is coming from the alternator area or perhaps the small pulley next to it (looks like its made out of fibre?). I used the highly technical trick of strategically placing a long screwdriver at various points and listening with my ear pressed to the end of it. I'm concerned that its a bearing about to let go. Has anyone come across this before? Its definately a rattling vibration rather than a whine. The car has covered 108000 miles by the way.

 

[SidewaysSteve]

With that cover off, pop the serpentine belt off and spin the pulley you think it is manually and see if it sounds rough, if it is rough or wobbles then its most likely it needs replacing.

The belty is easy to remove and refit, all you need is a 22mm socket or a ring spanner to move the tensioner and allow the belt to go slack.

 

[sbloxxy]

Ok, an update on this one. Finally tracked down the source of the vibration to a noisy alternator. When the belt is removed, I can feel a bit of play in the pulley. Its not side to side or up and down movement but almost as though a little slack is being taken up when the alternator pulley is turned.
The pulley itself actually looks like a bearing. If this is so, is this replaceable or is it time for a new alternator?