I've also had a very noisy Fluid-o-tech pump in my BZ99, which also wouldn't push any water. After ignoring the noise for a few days, it stopped completely so I dismantled it in the hope of being able to fix it. Everything inside appeared good, apart from a loose rubber washer (very perished and broken) I found floating around. After searching for a diagram, I found it should be on the outlet end of the piston. It looks like it's supposed to stop the piston from "hammering" into the outlet end of the pump body. I replaced the rubber bit with a new one, and it seems to be working good now, and a lot quieter. I suspect my pump was damaged by being run dry for too long, and the rubber bit wore out and fell off (hence the very loud noises), eventually jamming the piston from moving at which point it stopped. I've since found the reason my pump ran dry - the water tank has a ball-valve on the bottom which wasn't being opened properly, and was starving the pump of water (I noticed a large air bubble in the feed tube, which wasn't moving). The reason the ball-valve isn't opening is because the bottom of the tank has warped upwards and the coupler to the ball-valve isn't fully engaging. I think I can fix this by raising the coupling upwards a few millimeters. I would recommend checking the flow of water from the tank to the pump.
