Sounds to me like you may have overheated the bearings. The problem with dollies is that when you are towing them you have the rear axle on an angle, therefore the pinion bearing is running dry at very high speed which heats it up and locks them on. I understand your need for a warranty, sounds like they might be setting backlash on the gears too tight if your getting a roar out of them. I use kijiji, which is the canadian version of craigslist. Ive always had good luck with rebuild kits but Im a Truck and Coach mechanic so I have all the knowhow to do stuff like that myself haha I see where your coming from though getting frustrated with it. All in all if you do go the brand new route yes your going to be $1000+ for a complete, but maybe take yours to a local trusted shop and get them to take a look at it. Might just need to be set up or have a new set of bearings put in it.