Its not rocket science. Even when elk are quite, if you get in their kitchen and you sound like a challenge then they are going to sound off....all good hunters know this. I think that most folks are referring to, is not hearing any of the locator bugles in the am or pm. I have been astounded by folks who during September, will randomly call in a drainage, here nothing call back and assume the elk are not there.
Then why do some bulls come in quiet and others freak out explain that are u an elk??? This year i got in ones kitchen and he was bugling back and racking $hit then with a different bull he didnt make a sound but was racking $hit... I believe it has to do with 1. Weather 2. Competition 3. Location/area
All bulls are different. One drainage can be on fire and the next one over may be dead (elk in both).
* Is a cow in estrus in one herd and not the other
* Competition from satellite bulls (the larger and more comparable the sattelite bull the more action there seems to be)
*Did the bull just move Into the area and is rounding up cows
*How many Satellite bulls are around that talk a lot
*The elk are elk and we may not know the reasons they do what they do.
One of the most vocal and aggressive bulls I've ever seen was a heavier 4x4 herd bull running the show. When all other elk seemed to be settled down his was letting the world know where he was. I think it Is kind of the same thing as a young guy beating his chest because of his accomplishment (sound familiar
)

I recall a situation where I had (all in the same small corner of a drainage)
a smallish 5 point going off every few minutes and chasing everything that looked or sounded like an elk, a 4 point that did not respond to any calling- and was actually mounting a cow, a 6 point and another bull that came in slow and silent, and 2 spikes oblivious to the whole situation.