[id10t]

Other signals in your area. There are 11 channels (only of which 3 don't have overlap), and microwaves, portable phones, wireless devices, etc. all share that signal space. And not just in your area - within 200-300 feet of you, depending on what the walls are made of. The AP turns on, finds a unused channel, and is good... until it gets contention for that channel and has to hop around and find one.

Try setting the channel to always be either 1 or 11 (*this* one goes to 11!) and see if that helps. If thats not it, there is a company with some "new" paint on the market that has micro particles of metal in it, which basically creates a Faraday cage out of the room if you paint all 4 walls. (no joking) Of course, your portable phone won't work in the other parts of the house...