i know this had been done...but have i lost it?

[What's_nitro?]

It's just electrical noise from the motor, so it's not your diff about to explode or anything.

In my experience this is pretty normal. Outrunners make lots more noise than inrunners; I think because there is more EMF turbulence inside them. When you put more load on it (accelerate) the fields get stronger and so does the noise.

Though if it feels laggy, maybe try 20% PC? As long as the batteries are still "good" I don't think they are the problem.