After the plumbing install this weekend I shut down the return to feed and noticed my check valve was flapping and making a loud noise similar to a helicopter....."quick, get to the choppa". 
I can see the flap bouncing back and forth for a short while, then the overflows make a similar noise then it stops. kind of like dribbling a basketball then stopping and watching it bounce faster before it stops bouncing.
Im not familair with check valves but im sure this isnt normal. All I can think of is the flow thru the sump is faster than the back pressure from the return line and makes that noise until it is equalized. Maybe I need to adjust my overflows? I have those dang megaflow overflow kits but havent adjusted the standpipes fully yet.
Grouper Therapy - I hear you run 3 CV on your setup I would love your input

I can see the flap bouncing back and forth for a short while, then the overflows make a similar noise then it stops. kind of like dribbling a basketball then stopping and watching it bounce faster before it stops bouncing.
Im not familair with check valves but im sure this isnt normal. All I can think of is the flow thru the sump is faster than the back pressure from the return line and makes that noise until it is equalized. Maybe I need to adjust my overflows? I have those dang megaflow overflow kits but havent adjusted the standpipes fully yet.
Grouper Therapy - I hear you run 3 CV on your setup I would love your input