Sorry can't seem to work the search function good enough.

Have 16reg mk3.5 1.5tdci focus. A decent rattle just started from engine and battery warning light came on. I guess the battery warning light usually refers to alternator fault but could the rattle be related to that please?

Thanks

Check the alternator belt first, could be the belt tensioner failing. 

The battery won't generally be charging while the light is on.  It will eventually run out of power and the engine will cut out during a drive with no power to the fuel pump & injectors.

Thanks for replying you’re probably right,i’ll get in touch with garage monday, i wont be able to fix it anyway&not driving it as it is.

Just had quick look couldnt see obvious belt problem but i think everything packed in too tight nowadays but noticed a split in black plastic pipe just in front of coolant reservoir.

1 minute ago, Peterco said:

Just had quick look couldnt see obvious belt problem but i think everything packed in too tight nowadays but noticed a split in black plastic pipe just in front of coolant reservoir.

Ah, sounds like you're on to something there.  That's probably a coolant pipe.  If the engine is low on coolant it will get hot and rattly.  If the coolant was pouring out over the alternator it may have been damaged.  Can you post a picture of it?

Meant to add-thats the front of coolant reservoir you can see. The temp guage didnt rise. I’m no mechanic etc but checked oil/water levels they look fine. There was a ‘hot’ smell when i switched engine off last night.

Ok, that's not actually a coolant pipe.  It's just a bit of plastic protection over the wiring loom.  That split is perfectly acceptable.

Back to the drawing board with this fault...

Ok thanks

Update-belt had gone&new alternator needed. Cost just over £300.