You may have an air-gap faucet due to the specific plumbing codes in your area. This is a normal sound of an air-gap faucet.
Other causes may if you have your Drinking Water System installed under your sink. If it is a gurgling sound, that is the sound of the rejected water discharging from your system down your drain as it is making more purified water. This sound should occur only after using your system, until it refills the storage tank
