strange basement smell

Could be that you have a floor drain or two with a dried-up trap, and the low pressure created by combustion, and venting the exhaust gases, is pulling sewer gas up out of the drains. Try pouring a bucket of water down every floor drain you have, and see if that takes care of the problem. Repeat monthly.

Could also be that one, or both, is not vented properly, and you're getting a buildup of exhaust gases in the basement. If pouring water down the floor drains doesn't help the problem, get yourself a carbon monoxide detector/alarm and install it ASAP. (That's a good idea anyway, if you have gas appliances. Even if there isn't anything wrong with them -- yet.)

By "strange", do you mean smells kind of like rotten eggs? I can't image why Doug didn't ask this first.

-Kevin