|Sounds like something is stepping on your frequency. |
First unplug and power down any cordless phones you have, not cell phones, but house phones.
Install a wifi sniffer program, I like netstumbler. Now scan your area and see how many other access points you can see and note down the channel that they are broadcasting on.
Most routers default to channel 6, so if you and all your neighbors are on ch. 6 then you will have some interference. The best channels to have is 1 or 11, this will leave you with unallocated side bands.
Or it could be something stupid like your wireless card drivers. Just a thought.
Let me know if this helps