Ive noticed this on a few occasions. After I fire up the motors, and slowly raise the throttle, I can hear a high pitch squeeling for a second. it only does this at a certain RPM, and the range is very narrow ..... In other words, It may do it at 1400 rpm, but not 1450, or 1380 etc. I can feather the throttle to try and hit that RPM to hear it, but its easy to go over or under that narrow range that it makes this noise... You think it may be a motor about to fry out?