Sewage Pump stops with a THUD

My sewer line leaves the house well above the basement floor. To compensate for this, there is a small pump in a sealed chamber that takes any water from the floor drain and pumps it up to the main sewer line. I recently had a flow-through humidifier installed. This causes the sewer pump to run several times a day. Everything is great, until the pump kicks off with a really loud THUD.

Coming out of the sealed sump, there is a check valve immediately followed by a ball valve. Then there is about 6' of vertical pipe before it turns and flows into the main waste line. All of the pipe from the sump to the main waste line is 2" PVC. I'm pretty sure the pounding has to do with the check valve slamming shut. I'm really concerned about damaging the pipes. Does anybody have any suggestions? The slamming is driving my wife nuts...and you know if your wife isn't happy, nobody's happy!

Thanks!

You are likely correct, this is a common problem with many check valves. They make check valves that don't hammer.

http://www.aymcdonald.com/geninfo/aymc_silentsump2.pdf

That A.Y. McDonald valve is your answer!

Good call cacher chick!