Sounds like something isnt right if its rattling. Did you look at the alternator to see if the bearings are going on that?

Thanks Dandle, I didn't take it off but I did put my hand to it and it seems ok. There is the slightest movement out and in but I think that's normal, isn't it?? I was happy enough at the time that it was ok, I mean it didn't feel like it the bearing would be vibrating whie running. Might merit a closer look though, thanks..

Not sure if this is related to your problem but, I had a rattling sound comming from somewhere round my drive belt area it got worse over time, drove me mad. Turned out to be the Alternator clutch pulley that was slightly loose after some close inspection.

Alternator clutch pulley..?? Not sure I know what that is but I'll take the alterntator off and have a good look at the bearing and all... Thanks!

I had same problem mine turned out to be the water pump, the mechanic i used who is a good friend of mine took the belt off grabbed the drive wheel for the pump and it was solid no play what so ever, the same as all the other pullys, so he put the belt back on and the noise was still there so he got a long screwdriver placed it on the water pump whilst the engine was running and placed the handle of the screwdriver to his ear, and could hear it rattling, he then took the belt off again, took the water pump off, and sure enough the imprellor on the inside had come away and was travelling up and down the spline of the inside making the noise.

I think you will find you need a new alternator pulley it should incorporate a one way clutch so if you turn the pulley it will only drive the alternator in one direction and slip in the othe rdirection . If it drives both ways when you give it a sharp twist in eaither direction it would be siezed .. It will need two special splined tools to undo it and MAY have a left hand thread depending on which direction it rotates .

To be honest i dont know about the belt as i said my friend carried out the repair on mine, but i would certainly try the screwdriver test as it cost nothing that way you will know for sure if it is the water pump or not. Just to add the noise on mine used to come and go.