Q: AirPort drive intermittently dropping off network

I have an AirPort Extreme and have attached a 1 TB drive via USB. My husband and I use this to store files and back-up our Macs. The problem is that it drops out of the network every few days. I mean, it is not discoverable on Finder or in AirPort Utility. If I do a soft reset, it will magically reappear as if nothing happened. Not the biggest inconvenience, but also not the ay it is supposed to be working. It is certainly not the way it used to work. Have I screwed up a setting?