Coincidence, I've just had mine investigated for clicking/slapping,,,,,,, and it's the alternator pulley,
it had some slackness in it, job done. DAVE.

jules wrote:

That slapping of the belt on the tensioner pulley is very characteristic of a worn overun alternator pulley (OAP) - it works like a freehub on a bicycle - allowing the alternator to continue to spin fast when the engine slows down. When the OAP fails it drags the alternator down and puts a lot of extra tension in the belt causing the tensioner pulley to jump about . The OAP is easy to test with the AUX belt off.
You need a special tool (not expensive) to remove it from the alternator though - to hold the alternator shaft and turn the OAP separately.

M10/33teeth tool



The idler and tensioner pulleys are easy to replace (ive just done mine).

Hi O-B...

No, I didnt replace the alternator pulley, though I bought the tool (£6). When I replaced the FEAD belt pulleys and I then determined that the fault lay with the AC compressor and the alternator pulley seemed fine.

So I'll cross that bridge another day. Jules