What type of prefilters do you use?
I just bought 2 from a LFS in FL last week. One of them looks like a bag, my overflow tube goes into it. This one really cut some noise out and minimized the swirling and bubbles into my sump.
The other is just a sponge, I folded it in half and wedged it between the glass and return pump intake. It didn't seem to affect the inlet flow at all. I just added them Saturday. The overflow prefilter is already yellow.