From Pat Hasting's book, Another piece of the puzzle: Puppy Development:
Since this is the first time the puppies have use of all of their senses, they now need a stable environment and the influence of a stable dam. Sight and hearing are functioning well. A variety of noises (music, radio, bells, vacuums, etc) and sihgt (change in light level, moving objects and vibrations) should be part of thei daily life. The exposure to sudden loud noises must happen during the 3rd week when fear has not yet developed. The startle response should be encouraged so that the pup will startle and then return to normal on its own-something it must be able to do throughout its life.
...The puppies will begin "play-fighting" during this week, with a loose pecking order starting to form, Barking increases.
Yes, we've noticed all of these things and more. Most of the pups escaped from the warming box while I was changing the pad in the whelping box and even explored the room! Now they ge put in a crate while we clean the whelping box. Their first experience being crated. They are also quite vocal, barking and growlingm and I think they like to hear the sound of their own voices.