Bama,
One thing is for certain...you will feel the drumming in your chest, like a good percussion instrument, long before you will hear it.
The resonance will get deeper, the pitch lower and the hairs on the back of your neck will rise as the indistinguishable sound grows in intensity.
When their on their way in, in strut spittin' & drummin', I merely close my eyes and feel the sound in my chest.
That sound and intensity is comparable to only the opening morning's first gobble and the year's first wood thrush whistle...
Keep listening, and tell gobblinbuck to get you a bird....