Eheim CompactON 1000 pump makes ratling noise after startup

[niels123]

My Eheim CompactON 1000 is placed inside a tank of water in a lab and (in principle) running 24/7. However, I notice that when I unplug it I have to plug and unplug it several times until it goes quiet. The first few times I plug it in, it makes a ratling sound that is quite loud. The sound is also present when there is no air in the system and all hoses are filled and underwater. I'm curious to know what that sound is and if others have seen it too.

 

[SPR1968]

I have one and it’s pretty quiet but I seem to think when it starts, it does make a rattling noise.