I can’t sleep because of my expansion tank! Help

I just moved into a brand new condo and I live on the first floor. Directly beneath my bedroom is 3 water tanks and 1 expansion tank. Not every night, but most nights I am woken at least 3-4 times with a loud thumping noise. There are 2-3 thumps in a 1 second time period and then I will not hear it again for a couple of hours. As it gets colder here in New England it seems to be happening more often. I think I have isolated the noise down to the expansion tank but I am not 100% sure. Could this be the expansion tank or something else, and if it is the expansion tank does this mean the diagram is bad?

Any help is greatly appreciated…… thank you.

Stephen in Boston.

It could be pipes that expand and contract.
They can make noise as they cool.

With 3 water heaters you should have at least 2 maybe 3 expansion tanks...but it could be the water lines like Terry said...do you know if the water lines are copper?

tanks

There is nothing inside an expansion tank to make any sound, but they can be causing something else to make it. And, since an expansion tank only "operates" while the water is heating, it is unlikely that the water heater is turning on in the middle of the night when you have not taken a shower or used ANY hot water.