It's unknown exactly how motorLoad is measured and/or derived. I had assumed that it was a current measurement. But, then my motor head guru explained it was more complicated than that. I've been involved in 3 or 4 situations where there was a gradual degradation of a motor/ESC. In all of these situations the P3 was saying ESC error before it was readily apparent by looking at the motor data that DatCon knows about. In one case the P3 would indicate ESC error and shutdown after the 2 burst sequence at motorStart. This would happen more and more often.
@Luap finally noticed that one motorLoad would intermittently go to 0. The point being that the P3 was much better at detecting an ESC issue than a couple of flight analyst wannabes looking at a .DAT.
On the one hand I agree with the posters here that say there isn't anything to worry about if your P3 flies right and there are no error messages. But, if it's making a different sound I'd wanna know what's up. Is it possible that one of the props is dinged and you're hearing the effects of that? If you haven't already maybe you could try running it without the props and see if still sounds like there is a problem.