well, my buddies new 351 had a definate noise... it was more of a clatter and it was loud. A little tick is normal but if it just started and its pretty loud, I would look into the valve lash. Its a simple check so you might as well start there.
Since its hydraulic, its 0 lash. Turn the motor over until the intake vlave has opened, closed, then the exhaust has opened and closed. Once the have both fully opened and closed, turn the motor 1/4 turn to ensure you are on teh backside of the cam lobes. The pushrod should not be able to move up and down (lash) yet should be lose enough to spin. Check it out, its worth a shot