I realize that typing this is basically going to make me feel like I'm typing to a brick wall, but I'm sure somebody will appreciate it. Let's take a look at Millennium Force. This vantage point:
is from Frontier Town. One can clearly hear riders screaming on the first drop from this spot in the park. Can one hear riders screaming from any other portion of the ride? Absolutely not! Not only do riders not scream anywhere else on the ride, but if they were to, their screams would be directed in a different direction. Let's also not forget the fact that there are trees, buildings, other rides, etc in the way. Let's look at another angle:
From the queue line, one can clearly see the first drop in the distance, yet one cannot hear screaming riders while queuing because their screams are directed in the opposite direction.
As already stated, the tunnel was added so rider's screams cannot be heard. It's been added to the first drop because for almost everybody, the first drop of any ride is the most terrifying part of a coaster. Nobody is going to be screaming on one of the giant fan turns and even if somebody did, their scream would be directed in a different direction. Whatever is in that direction probably has a 9:00am-5:00pm weekday schedule. As already stated, football games are on Sundays. Whatever business won't be open on a Sunday. Stadium noise for a Monday Night Football game or Thursday Night Football game will be irrelevant cause it's obviously at night.
So yeah, screaming is a factor, regardless of how noisy the ride, park, or stadium get.