i had this on my e4 old aux belt started squeeling so fitted a new one and with in 2 days was squeeling again :0(
took it back off and found a small amount of rubber/dirt in the bottom of the grooves of the steering pump pulley .very hard to see at first
cleaned out with a small pick / screw driver and problem solved .
thought it was my tensioner but just crud making the belt skip :0)
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