Airport won't work when time machine backup drive is connected

I have an external iomega hard drive that I use for my time machine backups. When it's connected to the computer, airport stops being able to pick up my wireless internet connection. If I eject the drive from the computer the internet works fine again even if I don't physically unplug the drive from the USB port. What could be causing this to happen? I have a couple other things on the external as well. Just a few pictures, movies and game files. Thanks for the help!

edit: I'm running mac os x version 10.6.8 on a 2.4 GHz Intel Core i5 15" Macbook pro (4 gb 1067 mhz ddr3) that I bought in summer 2010