We almost built with Shaw four years ago. Luckily, they pissed me off before I signed a contract. My neighborhood is built probably 40-50% Shaw homes. There have been several complaining about them and not honoring their warranty or bullshitting the customer telling them it is normal. One of the biggest complaints is windows leaking. One of my neighbors had hard woods ruined by rain penetrating the front window. Shaw said it was because of the Oklahoma wind-driven rain and not covered under warranty; contact your insurance. Funny, it was maybe ten MPH winds that 'drove' it through the sills.
The wife works in home health and she hears many of her patients complaining of Shaw homes as well.
With all the complaints of my neighbors, I'm glad we didn't build with them. My builder went the extra mile and only charged cost for things (he said his profit is in the price of the house, not addons) with no change fees unless he had already ordered the items and had to pay the supply company a restocking fee.
I definetely think its a wind related incident. We have 1/2 acre lots with NOTHING between them.....and they are almost all backyard. Spring's a comin, so we will find out sooner than later if it is resolved.
@Gunbuffer, i believe it vents to the attic, but i'll have to double check. I did double check if it was drawing anything when running and it definetley does.