rap at

rap at something

 and rap on something
to tap on something to attract someone's attention. Who is that rapping at my door? Someone is rapping at the window, trying to get my attention. I will rap on her window and try to wake her.
See also: rap
References in classic literature ?
That is another point (replied he;) We must not pretend to determine on what motive the person may knock--tho' that someone DOES rap at the door, I am partly convinced.
The tea things were brought in, and already had Marianne been disappointed more than once by a rap at a neighbouring door, when a loud one was suddenly heard which could not be mistaken for one at any other house, Elinor felt secure of its announcing Willoughby's approach, and Marianne, starting up, moved towards the door.
A rap at that time of night and in that weather might have surprised an ordinary mortal who had dwelt two years in the gulch without seeing a human face, and could not fail to know that the country was impassable; but Mr.
A rap at this moment sounded on the door of the cosy apartment where Phileas Fogg was seated, and James Forster, the dismissed servant, appeared.
It came presently into my thoughts to rap at the glass, as if I wanted to speak with somebody, and if anybody was there they would be sure to come to the window, and then I would tell them to remove those rings, for that I had seen two suspicious fellows take notice of them.
She was growing interested in her occupation of picking out the aria, when there was a second rap at the door.
Researchers evaluated plant-produced mixtures with high RAP content (25 and 40 percent), different binders (PG64-22 and the softer PG58-28), and a control mixture with no RAP The study improved the understanding of the performance characteristics of hot-mix asphalt (HMA) mixtures with RAP at high, intermediate, and low temperatures and examined plant-produced HMA mixtures containing RAP.