I recently bought an older bungalow house built in 1970s. The piping throughout the house is copper and when I turn on my main floor bathroom faucet I hear a knocking sound coming from the pipes. What can I do to solve this problem?

Try turning the fuacet on very slowly and let me know if you still get the sound. Most likely when you turn the fuacet on fast, there is one or more pipes in the wall or under the floor that are bouncing off something, cuasing the knocking sound. You could try to locate the pipes and secure them better. Let me know what you find.