Jens, Thanks for the assistance, you've pointed out a couple new items for me to look at (okay, several). I still have a couple of questions. The return line (from the bottom of the fluid resevoir) which supplies fluid, collapses badly, but the sound is definitely coming from the pump area. I agree that there is a flow problem. Also, I've never heard of the resonator. Is that the ball shaped mounted aft of the resevoir? Do you know offhand the part# and/or where I may purchase one on line. Is replacement easy? Sincerely appreciate your advice. Oh, and can you recommend an easy method to bleed the system?