After I flush the toilet and the water went down the drain, a few moments later I hear a loud banging noise from the basement. I did some reading and it is suggested that I may have a water hammer. However the water hammer is normally associated with a closing valve which is not the case here. The toilet valve closes after the tank is full. I am thinking that it may be related to the drainage pipe rather that the water supply pipe.
Thank you for any help.

So you are saying that you are 100% sure the bang does not coincide with the fill valve stopping the supply to the tank, right? There is a chance that your drain pipe is lossely supported and the waste water slams into a 90 turn causing a bang but I think that would happen before the fill valve shuts off. Can you give us a time line in sceonds from the flush to the bang to the fill valve closing?

It's probably 1 second since the tank water went down the drain and the bang noise happens. I hear the bang before the valve shuts off so it is not likely water hammer.
And what makes the diagnose even harder is that the basement is finished so I have no access to the drain pipe unless I break the wall.

It does sound like the waste water is slamming into a turn in the drain but you are stuck without being able to get into the wall. Maybe someone else will jump in with additional thoughts.

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Originally Posted by ballengerb1

It does sound like the waste water is slamming into a turn in the drain but you are stuck without being able to get into the wall. Maybe someone else will jump in with additional thoughts.

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Yes, that is my feeling too. The question is how long can I live with this? Do I need an emergency repair? Am I going to get a flood soon?

If it is what I picture it isn't likely to cause a leak. Will you get used to it, probably not because you are always going to want to get to that fix it part of the problem.

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Originally Posted by ballengerb1

If it is what I picture it isn't likely to cause a leak. Will you get used to it, probably not because you are always going to want to get to that fix it part of the problem.

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Thank you bellengerb1. I really appreciate your help. However, what does seem to be the problem? Why I developed this noise?

It is possible that the pipe hangers that held the drain pipe have loosened over time. That could allow the pipe to move evn just 1/8" enough to make a thump againist the floor joists.