Vibrating/Humming copper water line??

I just recently tapped into my main water line b/c we just installed a sprinker system. I used a "T" to go off the main line. The problem I'm running into now is that when ever I run any water in the house, (faucet, toilet, etc.) the pipe makes this almost constant pulsating humming/vibrating noise.

I have a shut off just off the "T" so I can drain the line during the winter and when I close this valve it doesn't make the noice anymore.

There isn't any leaks of any kind but make the vibrating/humming sound when just running the house water...ANY IDEAS??

noise

IT is probably your backflow preventer, you did install one I hope. It sounds like the same noise a backflow preventer on a hose faucet makes when the faucet is turned on but the hose nozzle is shut off.

thanks for the info

actually,

there is a shutoff before my backflow preventer and it still vibrates when I shut it off. could it be a lack of pressure? it seems like the vibration is coming from the "T" that i used to come off the main water line.