thats the 55, my 125 is the same. very little noise in both tanks, No gurgle at all just water noise. My return pump is what I hear more then the overflows.
You can adjust them so its easy to adjust to get rid of any gurgle. You need a good return pump to keep up with the flow also, if the water level drops this is when a gurgle can occur.
My 125 had some noise but it was a easy fix, I took a 12-15" piece of airline and stuffed it into the overflow through the screen and down the over flow so that only a 4" piece was sticking out. What this did was allow air to pass through the hole better and the gurgle was gone. This happened after i had to switch out my return pump and the new one had a lower flow rate.
I like the look of the tank with this set up.. No big items in the tank, no OF box to lose siphon.
Diamond bit hole saws can be bought on line in many places..
Before drilling check and make sure the tank is not tempered. I have a 55 that I got from walmart and myself and the LFS
figured it was only tempered on the bottom... We'll we found out it was tempered glass on the whole tank... BOOM...
check with a Glass dealer in your area and see how much they will charge to drill a hole. Maybe worth it to have them do it with a drill press. Check around also, I had places tell me 50 a hole and I had others say 15.