My car is sounding like a tractor when idling, put my foot on the clutch and the noise goes. 

Two possibilities I have been told are, the alternator or thrust bearing. 
 

With my limited knowledge and good old YouTube I have managed to work out that when the belt is off and I have a screw driver in the alternator the freewheel pulley does not spin either way which I believe means that it is knackered. No charging or starting problems.

Would it be sensible to buy a pulley and the two tools needed to change it or could there be something else that I am not thinking about?

 

For others with the same problem. I changed the freewheel pulley and now the noise has gone. Pulley was 20 odd quid and the tools 16.