Most likely, you won't be able to draw any conclusion from the noise. Any electrical impulse of the same general shape and amplitude will make noises that are so similar that no one could tell them apart by sound. It's the waveform and shape that holds the information, not the noise made when you hook those currents to a speaker. If there's noise, there's current flowing. No noise -- no current flowing. You decide which you'd rather think about.
Personally, I'd ignore it. As nearly as I can tell, the noise is meant to be an audio indication that the needle has been placed in the correct place. Don't want somebody probing tender flesh with a sharp object to keep looking away from his target to make sure that he's actually getting the information that he's trying to get.
You may feel differently, but that's my $0.02 US. The best indication of whether or not ALS has spread to your arms is any new weakness you've found there during the past few weeks and months.
