From Handbook of Birds of Eastern North America by Frank M. Chapman. 1966. p 237:

“Of all the characteristics of this superb game bird, its habit of drumming is perhaps the most remarkable. This loud tattoo begins with the measured thump of the big drum, then gradually changes and dies away in the rumble of the kettle-drum. It may be briefly represented thus: Thump—-thump—-thump–thump, thump; thump, thump-rup rup rup rup r-r-r-r-r-r-r-r. The sound is produced by the male bird beating the air with his wings as he stands firmly braced on some favorite low perch, and it is now quite well known to be the call of the male to the female; an announcement that he is at the old rendezvous–a rendezvous that has perhaps served them for more than one season, and a place that in time becomes so fraught with delightful associations that even in autumn or winter the male, when he fins himself in the vicinity, cannot resist the temptation to mount his wonted perch and vent his feelings in the rolling drum-beat that was in springtime his song of love. But now, alas! there is no lady Grouse to come, shy but responsive, at the sound of his reverberating summons.”