Why is there a loud humming type sound in the pipes whenever water is being used from a faucet or from the toilet which just started recently in a year old townhouse?

It may be a mild water hammer. You may want to install an arrestor. A water hammer arrestor can be purchased from most hardware or Plumbing stores. Or you could just put in a T in a line. The T would need to be installed verticality with a cap on it. Water does not compress, the air in this dead end T will act like a spring giving the flowing water some cushion.