The Sonos wireless still uses Wifi, so it is the same as having 2 wireless networks runnng in the same area. You need to switch one of them to different subchannels.

Does the Sonos need to use wireless at all? I've seen 2 cases where "installers" have put in Sonos systems with wireless points, etc ,where all the remote devices and the serving computer sat right next to ethernet network points! If this is the case, ditch the wireless bridge and just plug them in.