Airport Expres & Air Tunes Problem

I have three airport express bas stations. Two newer ones (802.11n) and one older one (possibly first generation - certainly not "n" enabled anyway). I have them set to join my wireless network which is running through an Orange Livebox so I can have music played via airtunes in various rooms of the house. Whenever the microwave oven is used in the kitchen, the airport express unit that is in the kitchen immediately cuts out and goes to "blinking orange" mode, but it also takes out the base station in the lounge? Both of these are the newer "n" enabled units. However, the older airport express unit carries on fine?? It is equidistant with the unit in my lounge to the microwave and airport express unit in my kitchen. I also have a dual band II time capsule solely for backup purposes and this remains blissfully unaffected!

My questions are as follows:
1. Is the microwave oven interference a common problem and is there a way around it (other than not using the microwave!)
2. If my older airport express unit remains unaffected, can I "down grade" the newer ones to say a wireless "g" mode to see if that helps?
3. Am I being a complete techno spaz here and missing something completely obvious??