When I take a hot shower, the water pipe start making a humming noise and then after a while it start to shake and make a loud rattling noise. The shower is on the 3rd floor in a 3-storey house with a basement. This noise goes away when I decrease the temperature. What could be the problem?
The shower mixing valve may be defective, or you may have debris in your shower head causing excessive backpressure. As you eliminate hot water, you also reduce the flow of water in some valves, and that may be the reason the vibration goes away.
First, remove the shower head and run the water. If the vibration is no longer present, the shower head may need to be cleaned or replaced (some have small internal passages and are very hard to clean). If the vibration continues without the shower head on, the cause is likely to be the valve itself. Most mixing valves have a replaceable cartridge. To remove it, first turn off the water at the main service entrance. Remove the handle, usually by prying off the small cover plate in the center of the handle and removing the screw. When the handle is removed, you should see screws to allow the escutcheon plate to be removed, revealing the plumbing. The cartridge may unthread with a nut, or have a c-clip to remove to allow the cartridge to pull out of the valve. Take the cartridge with you to match up the correct parts at the hardware store. It is a good practice to take digital pictures of each step to aid in re-assembly.