My current outside sillcock is dripping from the faucet and there is no in-line shut off valve. My plumber recommends replacing the sillcock with a frost free sillcock but not installling an in-line shut-off valve. Also, the pipe vibrates when I turn off the water from the outside. Is there a technique that can fix the vibration?

My current outside sillcock is dripping from the faucet and there is no in-line shut off valve. My plumber recommends replacing the sillcock with a frost free sillcock but not installling an in-line shut-off valve. Also, the pipe vibrates when I turn off the water from the outside. Is there a technique that can fix the vibration?
The vibration is usually due to a worn washer, a loose seat or debris caught up between the washer and the seat.

I'd start with replacing the washer.