Hey Mark,

This is due to WiFi and Bluetooth using adjacent / overlapping radio frequencies.

This had me really stumped when I first got my headset. I almost broke the thing trying to "fix" it!

What gave it away was the perfect sound quality when I tested it in my car, even though I was actually much closer (~2 meters) to my WiFi router. (I guess this was due to the car acting like a Faraday cage shielding most of the WiFi.)

Odd thing is the bluetooth VoIP phone supplied with my Acer laptop works just fine, with Bluetooth & WiFi in active use of course. I imagine this is where it comes down to the quality of the radio transceivers used, i.e. A decent transmitter won't cause interference on neighbouring frequencies (harmonics) and a good receiver would filter these to a degree.