water hammer problem..help!

I recently took my pump from under the house into the garage by adding pvc to the black poly going out to the well. I have a check valve right before the pipe goes into tthe pump. The hammer is only in the main line going to the pump. You hear it when the pump cuts off. Sounds like a loud thud. How can I stop this? What could be causing it?

I answered this in the other forum here.

Gary
Quality Water Associates