what was the out come of this thread a few weeks back, I can't find anything with the "Search" I have had the grrrr for about 2 years now. It only got worse after I installed the Slee castor plates. It also only makes the noise (sounds like wind blowing over a pipe) when the drive terrain has no load on it...going down hill (over 40mph) and backing off the throttle just enough to coast.