Audio drops out when I hit a light switch

I have a really frustrating problem. I've just moved into a new house and am experiencing audio dropouts whenever I hit a light switch in the house (many of the lights are fluorescent). The problem only affects my Bel Canto DAC2.

The dropouts only happen when listening to two-channel stereo. I'm using the coax digital output of an Arcam DV79 dvd player to the Bel Canto, then to an Arcam AVP700 pre/pro and on the CIAudio D-100 monoblocks. The dropouts never occur when just watching a DVD (I use the Arcam DV79's optical output for that) nor when watching cable tv. That is, the problem does not occur with either of the Arcam units.

Watching the Bel Canto, I can see the green 'signal accepted' light flick momentarily to a red 'no signal' light whenever I flick a light switch. The Bel Canto is the unit affected by the lights.

I've tried using a couple of different coax cables and an optical cable but it's made no difference. Does anyone have any idea what is going on and how to fix it? Would a high-grade power conditioner help (I'm currently using a mid-range Belkin surge protector/filter)?

Any help would be greatly appreciated.