That is probably a gear (transmission) whine. If it is a separate file just delete it or edit its volume to zero; otherwise it is incorporated into the engine sound and your only recourse is to start with a different sound.
It could also be a turbo whine, these are almost always incorporated in the engine sound, again necessitating finding a different sound to work with.
If properly done, gear whine is usually a lower pitch than turbo, is present at all speeds and increases pitch with speed; properly done turbo whine is higher pitch, should only be evident at mid and high rpm, and increases pitch rapidly with rpm.
With your car in neutral rev the engine, if you hear the sound you don't like it's a turbo; if you only hear the sound when the car is moving it is probably a gear sound. Look in the aud file for a reference to "gear" "gearbox" "transmission" and place a double slash - // - in front of that line, save and try the car again.