We've noticed something similar. It's like a VOX, or squelch. There's zero background noise, unless someone talks. If we increase the input level, the threshold that "breaks the squelch" goes down, and we'll hear a bit more background, but again, only when they're talking.
However, the quality is as good or better than it's ever been. Very natural sound. Just have to keep the input level high (more sensitive) so the words don't get clipped at the beginning and end of sentences. Overall, it's less tiring than having a lot of distracting noise during "quiet" periods.
All this is with "noise reduction" off. With it on, the quality is poorer.
I would like to see an option or adjustment for this. Even though I mentioned it being nice to get rid of "noise", I do miss having ambient sound from the other end. We use it for hours on end to visit with distant family, and the background sound is part of the experience for us.
I might look around and see if there's some hidden plist option. It's a good candidate for some feedback, too.