Lately my BOV has been making a strange noise, it's more like a KRRRR sound (really low pitched) as opposed to a ksshhh (higher pitched) when I change gears or decelerate. It seems to only happen when I get maximum 6-7 psi. Other times when I get 10psi (standard) this sound does not occur (don't really hear a sound) and I get full acceleration as opposed to slowly climbing.

Anyone know what the problem could be?

 

It seems to occcur less now that Winter is here (Australia) and there is cool air about.