Very very early in the am I have been woken by machine gun like noise coming from the wall. I have only heard it in the am. It does not seem to have any relationship with flushing the toilet or running water. It lasts for about an hour, then stops for an hour and then start up again for about another hour. Does anyone have ideas of what the problem is?

I have an idea that this noise is in some way connected to your commode or if you live in an apartment it could possibly be a neighbors commode. It could either be a loose washer in the water supply cutoff that goes to the commode or it could be the cutoff in the valve I the commode itself. You or your neighbor could be losing water through the flapper in the commode and at a certain point the commode will start to refill itself and since it is such a small amount of water entering the commode it causes the loose washer to vibrate making the noise you hear.
The next time you hear this noise do two things. One is to feel of the line that goes up to the commode tank. The other is to take the lid off the commode tank and lift the float rod, or the float mechanism and see if the noise stops. I hope I have helped you. Good luck.

Couldn't have said it better myself Letmetellu. Great explanation of "seat chatter". Feel the flat part of the flapper. If it has wavy or rough edges replace it. Another cause might be the tank level. If the level's too high it can leak over the top of the overflow tube causinhg the ballcock to kick on. At one point the seepage from the overflow tube and the filling from the ballcock will balance out and the vibration will begin. The tank level should be 1/2" below the white overflow tube when the tank's filled. Good luck, Tom

Thanks for the help, but the noise is not coming from anywhere near the bathroom. It is close to the baseboard water heater.

Ahh! Then let me move this over to the heating page. Regards, tom