I have a water pressure regulator that occasionally makes a very loud noise when I am running water inside the house. The regulator seems to be working properly, incoming pressure is about 100psi and it reduces it to 45 psi into the house. Do I need to replace the regulator to get rid of the noise? It is only 6 years old.

Sounds like you're getting a little seat chatter, Try adjusting the PSI up or down and see if that doesn't help. Good luck, Tom