iMac - Airport 'Looking for networks' affects FireWire audio device
Other than disabling the WiFi card entirely, there isn't a documented way to prevent periodic scans with the Mac OS running.

It's possible that just normal interference like when a mobile phone disturbs a radio is affecting the audio signals.  You don't say what Mac hardware you are using, but you could try something as simple as moving the audio hardware further away, or to the other side of your iMac/Macbook etc, maybe even run it through a hub or use a long cable to take it out of reach of the antenna, see if it makes a difference.  Failing that try changing the WiFi channels on your router to see if it helps.

The other issue to consider is perhaps the AirPort card is failing or improperly grounded / connected inside the mac. I have seen the antenna cables pop off when a Mac takes a tumble - so if it's not too much inconvenience or cost, having a technician run a quick test on the airport card and verify all the internal cables / grounding is correct might solve the issue as well.

It's entirely possible with Lion that the airport drivers do different things with AirDrop that Windows drivers don't do and that could conceivably be the cause. It's a long shot, but I've seen this sort of thing before.