My pumps have just started to sound like cement mixers- they grind for a few seconds then go quiet, then grind again- all I've done is drain one of my loops and refill- no movement to the pumps or reservoir Temps seem fine

Any ideas people as I don't want failing pumps to ruin my rig
should say that I have 2x D5 USB pumps linked to Aquaero 6 via aquabus and pumps are in a Koolance RP-452x2 bay reservoir and have been for approx. 18-24 months with no issues at all

update:
noise has subsided but now get knocking at random intervals- hope it's just air but have leak tested for hours

Update:
noise has gone but my gpu loop temps have jumped by 10c to around 47 + 56 c respectively- wonder if the pump is not working or AE6 not working to sense

Update:

seems to be fine now- temps back to 25+26c and no noise so hurrah!!!

That didn't last long- temps back up to 50c and above so unplugged everything and just tested pumps with psu and one of them does not work so a new one ordered and on the way