Wireless signal killer???

Anyone know of something that would kill the signal strength of base stations? I had to base stations loose their signal and they won’t come back in my building. I thought it was competing channels first, so I eliminated other devices like cordless phones etc. They work fine if moved offsite, but bring them back and they vanish…..

I have tried using a sniffer to track them down, and they will once in a great while show up…but only for a few seconds, then go back to 0 signal strength and then dissapear, with the base station sitting right next to the PowerBook!

Any ideas????