DAC drops out when Furnace starts or stops. HELP

good suggestions. Thanks. I will look into it tonight and report back with results.

OK, so I started by changing the digital cable (it was the easiest). I had been using an Audio Envy cable that I really like. Had it about one month. After inserting it into the system I had an occasional drop out but didn't think a lot about it. However as the cold nights came I started having more and more drop outs. Which lead me to tracking down the cause. Thus I discovered that it was the furnace and water heater making the disruption. Prior to the cold snap, it was only the turning on and off of the water heater that caused the drop out. But now with the furnace in the mix the drop out rate was increased signifigantally.
I replaced the AE cable with a Grover Huffman digital cable and last night experienced no drop outs.
The AE cable is only one meter while the GH cable is 1 1/2M.
Is it the length of the cable that could be the culprit or is it the design/construction differences?
Either way, thanks for the suggestions to get the gremlins out. I will also look into the service panel today to check the wiring as to which leg of the mains might be in common.

Thanks to all for the suggestions and info. After listening again tonight I have had no drop outs with the 2nd digital cable in place.
However I think "Almarg" has hit on the root cause.
I have been constantly fighting a ground loop hum that I cannot cure.
I have tried cheater plugs on some/all pieces of equipment, plugging all the audio gear into one strip, isolation transformers ETC ETC.
I have come to the limits of my knowledge of finding the source of the imbalance.
Thanks for the ground/neutral info from "Cdrc".
I think it"s time to call in an electrician. Hopefully I can find one who understands this type of problem.