Frank,
Interesting question. Some might argue that this is similar to the question if color and color schemes affect the way judges score. However, in my opinion, the two subjects are entirely different.
From my experience, I believe that engine/motor sound does make a difference in the way judges score. This factor might change over time as judges become more familiar with different powerplant sounds.
I was witness at a World Championships where I heard a judge complain that a particular piped ship flew too fast. (I have no idea if the perceived speed affected the score from that judge, but given the fact he commented on it, I have an idea it did.) During that contest, I timed the lap time of that particular plane. Surprise, surprise, it was slower than most of the unpiped ships at that contest. Now, did that judge feel the maneuvers were flown too fast to be able to judge accurately, I have no idea, but since he commented, I feel that the scores he gave were impacted.
As a judge, I know that there is a factor between hearing the "whirring" sound of the electrics and the noise/snarly sound of the IC engines - both unpiped and piped. I think that I have been "lulled" into how "pleasant" the electric pattern being flown (and even the 4-strokers) is compared to the snarly IC engines. I am aware, personally, of this going on in my perception of the pattern being flown. I feel, over the years, as I have become more accustomed to the different "sounds" of these contraptions and try to not let the noise, the type of noise, or lack of noise affect my score. I have no idea if I, personally, allow the sound to affect the score. I definitely try not to let it do so. How other judges react, I have no idea. It would take a considerable effort and time to come up with any kind of "scientific" analyses to determine if judges, either individually or as a group, allow sound to be a factor in their scoring.
I like to think that over time as all judges have more experience with these various types of power plants that their sound becomes less and less of a factor in their scoring.
This gets into the realm similar to when judges get "lulled" into a pilot's pattern where every bottom is consistently and exactly at 5 feet (squares and loops, pullouts of the wingover) and good scores result, almost regardless of sizes and shapes. National and World Championships have been won with that style of pattern. That does not happen so much anymore because top fliers are now putting correct sizes and shapes on those consistent bottoms, just like the rules require (though I think sizes generally can be improved across all levels of competition.)
Keith