Sump Flow

So when I picked my return pump I based it on 4-7 x per hour turnover rate, but I did that based on my total water volume display + sump.



Recently I read a post where someone said it should be based just on the volume of the sump, is that right? I'm thinking it must be since I've had to throttle the flow way down with a valve to get it to the point where stuff will settle. This has made my pump/return line vibrate like crazy and the noise is annoying...



I'm thinking its time for a different (smaller) return pump, can anyone recommend a good QUIET pump for a 40B with a 20G sump? It will have about a 3ft head to reach the display



Thanks!