Here in the hardwoods of west Tennessee during the early season before the woods greens up gobblers can sound closer than they are - later in the season the opposite is true, they are closer than they sound. All the leaves help absorb the sound. Humidity and wind can also greatly effect the volume of the sound you hear.

Gobblers sound much louder on the roost than on the ground. Gobblers facing you on the roost are much louder than if facing away.

Gobblers in the hardwoods sound much louder than an open field. The trees help reflect the sound around. In my observation, gobbles from a hollow sound louder than those from a ridgetop.

You're correct in that they sound different when really close. I call it a "rattle" that I can hear during the gobble.inside 60-80 yards. I make sure my gun is ready before hearing the "rattle" in the gobbler.

Of course, if you hear drumming get ready because he is very close.