If there is no air in the pipe, water can't slosh around. I have heard the noise made from the pipe or wire slapping against each other or the casing. This sounds much different than water hammer and usually happens on pump start up not shut down. The check valve is holding but, it is dragging. Probably worn out enough to be sticking in the wide open position. After the pump shuts off, the flow must reverse for a second before there is sufficient force to close the check valve, which causes the water hammer "thunk". If this is the case the only thing that will fix the problem is replacing the check with one that does not stick. Even the CSV won't help if the spring in the check is broken and the valve sticks wide open. The CSV would have kept this problem from happening in the first place as check valves are just one of many items in a pump system that is destroyed from cycling on and off repeatedly. I don't see how anyone can read a few lines from this forum and decide that you don't have a problem at all. So I guess you are being told that the problem must all be in your head. So I would certainly listen to this person when they tell you not to use a CSV. The CSV is one thing that might fix the problem without having to pull the pump. The CSV is the only thing that would have kept this from happening in the first place and will keep it from happening again. If you install the CSV in the well, you won't have to do any digging. You will however, need to pull the pump up far enough to install the CSV just under the pitless adapter. You would need to use a CSC1 coupling to make the CSV strong enough to hold the weight of the pump. Replacing the down hole check valve and installing the CSV would stop the water hammer and keep it from happening again.