tap at

tap at (something)

To strike something lightly, swiftly, and repeatedly. You're never going to drive the stake into the ground tapping at it with your hammer like that. I could have sworn I heard someone tapping at the window, but there was no one there when I got up to check.
See also: tap

tap at something

to make one or more light blows on something. Fred tapped at the door, but no one heard him. Who is tapping at my window?
See also: tap
References in classic literature ?
Bucketful by bucketful, from the tap at the sink in the corner, he filled a large galvanized-iron tub.
Carbide offers the potential of higher cutting speeds and lifetimes of 100 to 500 times the life of a conventional tap at about ten times its cost, Matysiak says.