172 phase 2 aux belt squeal on full lock

[Integrale1]

My 172 phase 2 has started to make a squeal when turning the steering to full lock when the car is stationary. Last weekend the car suffered an alternator failure. I replaced this and also replaced the aux belt with a genuine renault one.
The car had a new tensioner and idlers 14 thousand miles ago plus a new water pump/PAS pump ten thousand miles ago all genuine renault ones.

My question is does anybody have any ideas why its just started to do this? Also does anybody have an idea exactly how tight the belt should be. when i reach underneath the car i can feel a slight deflection in the belt, I'm beginning to wonder whether the new belt has stretched or the tensioner is starting to fail.

 

[RS Charlie]

Silly question but are the ribs all on the right grooves on all of the pulleys? It is easily done and I have done it before.

I'll check the deflection of my belt later on on the bottom run.

 

[Integrale1]

Yeah i am pretty certain it's located on all the pulleys correctly. It's only just started doing it yesterday, managed to cover around 300 miles before it made the noise. It only does it when the car is stationary, the belt is fine at all the other operating speeds.