Hey I am starting to lose it. Every night I hear light thumping noise. It is definitely rhythmic and mechanical, but I cannot figure it out... Not that I have any expertise on anything mechanical.

I hear it the loudest in the bathroom and in the laundry room (which is located in carport not near the bathroom).
I ruled out a/c because it was not running and I was not hearing anything loud outside...
I figured water or plumbing issue might be part of the equation, but no one was using the water at that moment.
We have gas and I did worry about something along those lines, but would have no idea what look for etc...

Any ideas?? We rent this home and I would prefer no to call landlord until I know what I might be talking about :)

Thanks!!

My bet's on the water heater and I'll make book that you don't flush your heater on a regular basis.

If you do not flush,(not drain) your heater on a regular basis it will build up mineral on the bottom of the tank. When the flame comes on it turns the water trapped under the mineral to steam and the steam escaping is what you hear. Let me show you how to flush your heater. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) and some white grains,(lime or calcium carbonate). The whole thing shouldn't take more then a few minutes. Don't forget to flush it out every month. Your heater will thank you for it. You might want to consider cleaning the screens on your aerators if you have a high mineral buildup. If the problem still persists after you have flushed, you will have to drain the heater, remove the boiler drain and go up in the bottom of the tank with a wood or plastic rod, (not metal) and try to break up the mineral and flush it out. Good luck and thank you for rating my answer, Tom

Thanks! Fantastic answer!
The thing is I don't hear anything near the heater... it is in the wall/ceiling of the laundry room and faintly in rest of house. You think it is the steam releasing through the pipes or such?

That could be one explanation. Another could be expansion and contraction.
Knocking, popping, creaking and crackling pipes are a common complaint, especially in colder weather. I can tell you what's happening and take the mystery out of it but you're not going to like the repair. When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight. Most people when they learn what causes it just elect to live with it. You must realize that noise and smells are the hardest to nail down if we aren't there to see for ourselves.
Good luck and thank you for rating my answer. Tom