What causes a buzzing sound in the hot water pipes (when tap is open)?

Um, this may sound like a silly question, but when installing plumbing it's a step that's often times overlooked...... Are your pipes mounted to the wall studs? Pipes that are not properly fastened to the studs to hold them in place will oftentimes give off horrible noises, from buzzing, to ratteling, to even banging inside the walls. The hot water pipes are the worst culprits of this because the water that stays in the pipes is most often cold (or has gone cold since there is no more hot water being forced through it). Then once you turn on the hot water, the hot water is being forced out of your water heater, up through the pipe, which causes the cold water to exit the pipe and the pipe to warm back up, thereby making all its racket. I hope that explains what might possibly be going on. If it is, you unfortunately may have to hire someone to come in to fix it, unless you're like me and not afraid of replacing a little drywall and learning about fixing some plumbing issues. If you need any more assistance please feel free to contact me. I'll be happy to help!

there is air in your pipes. it has a simple solution that wont cost you a single cent. go to where your water heater is, and at the bottom it should have a fawcet somewhere close to the bottom. from there you can open the water SLOWLY and drain some of the sediments in the water into a bucket. until the water runs clear. then close it . the heater will then refill itself. after that, just go to your sink/bathroom and let the water from the sink run a little while.. 2 minutes tops. and voila!! noises gone!!