Take the aux belt off start it up and see if the noise goes if it does it probably the alternator pulley
As above.
Since your obviously proficient enough to have changed the tensioner, you'll be able to change the pulley too.
It's a one way pulley, so once you've taken the belt off to check if the sound goes away, try to twist the pulley in both directions. It should grab one way and turn freely in the other. You'll need to jam something such as a screwdriver into the alternator to stop it turning when doing this, so just be careful not to damage it when you do.
The pulley can fail in that it can freewheel both ways, or grab both ways.
You need a specialist tool to remove it but it is very cheap. I bought mine for NZ$12, so about £5.
