Just wondering - these tanks like the AR620 where the filter is built into the hood, how noisy is the filter? Can you hear it trickling? Is it like the sound of a hang on back filter?

From my experience with an AR380 with this sort of filter, it depends on the water level in the tank. I would usually have my water level up high enough to touch the bottom of the filter box. In the filter itself, I run from the bottom of the box- small ceramic noodles, charcoal filter, then 2 layers of filter wool, makes it basically silent :-)

Cool, so the internal spray bar is just spraying straight onto the filter wool?

Yes onto filter wool

I have the 980 and the noise is minimal as long as it's keep relatively full the main noise issue is from water flowing back into tank

Im running a 980 also, did not find the water returning to the tank to noisy, more of a light gurgling/bubbling sound,

But I have now cut a bunch of 1 inch long 8mm clear pvc tubes and stuffed them down in the return duckbill/spreader, this quietened it down a bit more, will put a pic up tonight if anyone's intrested

Have an Ecostyle 61 which has the same trickle system and can confirm the filter itself isn't noisy, however the flow of water into the tank is.

The source of noise is water pouring from the tray into the outlet compartment which doesn't fill up very high, so the water drops a good few cm, resulting a gurgling and splashing sound. I've solved this by jamming some filter sponge in there to break the fall. Works surprisingly well, and actually filters a lot of debris too. Keep in mind that you will have to clean the sponge out every 2-4 weeks. After doing this you shouldn't hear any noise at all coming from the system.