Gator TS Noise

Hi,

I have a bunch of gator TS vehicles. These machines are loud but have a proud sound to them. One of the gators has a sound that when it's idling, sounds normal, but when you press the gas it has a loud whine or roar. The other gators have a nice put put sound to them. They all ride nicely, but was wondering if anyone had ideas as to what this whine could be. I can post an audio clip of what it sounds like