Screech when heater fan is on

I have a screech from start up from the aux belt.It goes

Away when warm but is there again when you put the heater fan on!



Am I right in thinking it's put more load on the belt ( I've just changed it but no difference)

I didn't change the tensioner though and possibly thinking it's that or alternator or ps pulley..??



Any pointers would be great... Cheers