Using the 4000 as a return for my sump as a dry app but very noisy upon start up.Could the micro bubbles be causing that?What could it be?Does it need time to warm up?It's right out of the box.
Oh,did'nt do that but Turned it off and off a few times,right now it's running quiet but it acts up sometimes.Might have to get a replacement if it continues.Running it externally.
I have the same pump - it's a rattlebox and often stops - I only use it to mix water and it has stopped on me 2x in the last month - I would reassess this pump as a return and consider an eheim or the like.
the rattle noise is cause by micro bubbles created probably from running dry initially. try turn it off for a few secs to allow the bubbles settle then turn it back on.
the reason it sometimes turn off is cause by a thermo sensor. it is design to turn off when it gets too hot. this is to prevent it from burning out. the pump needs to be in a well vented area.
I agree with reefman, when I had mine plumbed externally in a not well ventilated place I would have issues, but when placed in my sump where the temp is always stable it worked perfectly.
As for the rattle and noise, the pump does have to be primed(water in it), and even then mine made some noise on startup. I have heard of some people having quality control issues were one pump is noisy but after exchanging it at the store the next was dead silent, so maybe you should try that.
Good luck and don't forget to enjoy the tank