Arrrrrrrrrgh, bloody rattle..... 300tdi

I noticed a slight rattle under the bonnet a couple of weeks ago, came, went came back and got more noticeable. I bit the bullet and decided to take a look.

Water pump, it has to be the water pump thinks I. Craddocks, seventeen quid, bargain. Pulled the old one off and in its place now sits a shiny new one. The rattle is still there

Serpentine belt off, motor started, no rattle.
Serpentine belt on, motor started, bloody rattle.

Next step, replacement altenator or is it something that is common on a 300tdi that I am missing?

Ta in advance

Tensioner?

Have you put a penny in behind your tensioner ??

Hadn't thought of the tensioner

It is a mechanical rattle not the belt squeal

When I put my mush in the engine bay it sounds like it is on the right hand side

the tensioner has a bearing could be that that about to give up if it is replace it asap as that belt as you know drives the water pump. mine had to have a new engine when my mate owned it due to the belt coming off

Check that you haven't got a loose pulley

Checked each pulley, all tight so on a hunch I changed the alternator, hey presto a quiet Disco again. Now I have a spare who sells those kits to put twin alternators on