just went out for ride and noticed a noise from my BB as well. Bike is a Schwinn Fastback LTD with 1050 miles. Had same problem about 6 weeks ago and took to LBS and they disassembled and said something was not seated property. Bike at that time only had about 150 miles on it.
Now, its doing it again. This time I notice when I take my weight off the seat the noise goes away.
I weigh 283 lbs (down from 300 when I first started riding).
Looks like I am back to bike shop tomorrow.