I have been flushing my water tank to clean and sanitize it after having a problem with algae last year. As I was running the pump, I noticed that it was making much more noise than usual. I thought, "Oh no! Now I need to buy a water pump." However, my curiosity kicked in and I decided to take it out and see if I could figure out why it was making that noise. To be more precise, it was an intermittent noise that sounded like something rattling around in the pump.

I disconnected the hoses (after releasing pressure and letting the low point drains drain the system. I also bypassed the water heater for this since I did not want to deal with 6 gallons of water draining in the pump space. I brought it inside and took the pump head off the motor and discovered that there was a small washer inside. I have no idea how long it has been there. The pump has been quiet previously and this only seemed to start very recently when I started flushing the tank. I do have the strainer in place so I don't see how it could have gotten in that way. It looks like one of the ones that is used on the screws that fasten the pump head to the motor. At least I think it was in there. I don't think It fell of one of the screws as I was removing it.

After giving it a look to see if I could figure out what was rattling (if it was not the washer), I reassembled it and reinstalled it in our 179. When I turned it on (after putting all the valves I had changed back in the proper position) it primed and ran to pressurize. Then it shut off. It was quiet. I tried turning on and off faucets, and it continued to run quietly.

I thought this was an odd enough problem to deserve being written up in case anyone else starts having a noisy pump problem.  It is actually very easy to take apart and put back together, so don't be afraid to try it if your pump starts making a rattling sound.

p.s. I did not mess with either of the small hex screws as I thought they probably control the pressure at which the pump runs and shuts off as well as smoothing the water flow. I did not want to mess any settings up by turning either of them.

Quiet as in a low, steady sound instead of a rattling sound. It isn't anywhere near silent. It is, as you say, a relative term.

I do have a compressor. As for the RV antifreeze, I have found that even with compressed air, when I followed that by RV antifreeze, I see some residual water being pushed out. I don't go with 80 PSI. I limit it to 50 PSI. Also, using compressed air does nothing to protect the pump. That is one reason I use it. It is a personal preference.