Cheers for your help - I can't find any figures for the flow rate of an 003 pump to compre it against the others - does anybody know?

I've been out and looked at it again this evening. The pump intially starts off with an intermittant ZUZ...ZUZ...ZUZ which gets louder and more continuous after the car has running for a few minutes. It sounds a a motor bearing kind of noise - could this be down to cavitation?