There are only 3 non-overlapping channels in 802.11b/g. 1, 6, 11
If this happens with the router set to either, then you got a problem.
Everyone says 802.11a is a bad protocol, until this happens and they realize they have 13 choices instead of 3.
Anyway, you have a dirty spectrum in your house and since 802.11b/g uses the same freq as your microwave, your phone, baby monitor if you have one (or if the neighbors have any of the same). Either go to 802.11a or 802.11n where you will be avoiding the dirty spectrum by utilizing the a spec.