I have been trying to narrow down what is causing thumping sounds I hear in my home pipes that is always heard early in the evening. The sound stays the same if the water is running or not. The thumping sound seems to be less loud after a few hours into the evening.

I suspected the hot water pipes. I shut the hot water off at noon and ran water until it was cold. The thumping was dramatically softer that evening, but still heard it. I raised the water heater temp for the next evening and the thumping was louder than usual.

Any idea on what this could be and any way to narrow it down?

The strange thing is the sound seems to start about an hour or so after the sun has gone down. I live in Florida and have a well system. The home has a slab foundation and I can hear the thumping louder if I put my ear to the ground. During the day I never hear the thumping sounds.

Thanks for any assistance!