The pipes/faucet for our outside faucets vibrate when they are turned on (open) until a heavy flow is established, then it stops. They also vibrate when turning off the water as the flow gets close to shut-off. It does not seem to matter how slowly I open of close the valves, at low flow they vibrate. This only occurs with the oustide faucets. No inside faucet valves do this. Any ideas? Thanks

You have a loose washer at the stem inside your valve, shut water to the house remove the packing or the bonnet nut which one applies to your Spigot, remove the stem assembly tighten the screw if that would not help, take the stem with you to HD or Lowes’s get a new washer and replace it, see the images below, good luck.
John