Aux belt squeal

[markpw73]

Hello all,

I replaced the aux belt and tensioner pulley back in Feb this year but it is squealing again mainly at full lock esp when under load (aircon on).

I thought they were self tensioning types and i used OE Audi parts?

Anyone have any ideas what else could be wrong?

On a A4 avant 1.9tdi pd130 53plate

Thanks
Mark