Eheim return pump grinding?

[ams_reef]

My question in why is my Eheim 1260 pump making a grinding sound? It’s not constant but is louder for a few seconds then gets quieter. It’s currently connected to the return via Eheim vinyl tubing and is split off a tee going into an icecap algae turf scrubber. I’d estimate about 100gph goes into the algae turf scrubber and the rest to the return.

I pulled the pump apart and everything
seemed alright, impeller/shaft/etc all were
aligned and no debris was blocking.

The return section is very tight between this large pump and the tunze osmolator but vibration doesn’t seem to be the issue here. I own many eheim canister filters and I know Eheim pumps are quiet so I have no idea what is causing this.

 

[ams_reef]

I shut the valve off to the algae turf scrubber and all the noise disappeared. Then Eheim pump is completely silent now.

I guess the T off of the return caused this. I’ll grab a small Eheim compacton pump to feed the algae turf scrubber independently now.