Any time you create a spark, you are basically transmitting a signal. Spark plugs, welders, electric motors and such create interference of some sort or another. Most of this is choked by some kind of noise suppressor and you don't notice it. The welder sparks are not suppressed for good reason.

My 250EX makes my radio squeel, and on a high pulse setting it causes my cell phone to get warm in my pocket and messes it up. I have a friend with a pacemaker that will weld all day long in DC Tig and stick with no problem. When it comes to HF and AC welding, he keeps his distance from us. Even though some might say that it's safe, but why take a chance. Until there is sufficient data on this, he doesn't want to be a guinea pig.