Hi, I have knocking in my pipes when I try to get hot water in the kitchen faucet. Opening an upstairs faucet that's directly above will temporarily stop it. I cannot use my dishwasher because even when I get the knocking to stop, hot water won't get inside. I did get the knocking to stop by turning off the main water, opening all faucets, and flushing aii toilets. After six days the knocking came back. Several months earlier I replaced the water heater. What do you think is wrong and how to fix it? Thank You, Rob