Bummer about your smart. Hope whatever they find is under warranty. If not, I would be contacting "CarMax" IMMEDIATELY. "CarMax" DID show you the "CarFax", right?
I too can't imagine what it might be, squealing on start-up and continuing while driving? Must be something driven off the engine. Alternator maybe or just the drive belt?
Well, in any case, I hope you get your smart back and get on the road again. We've had great weather here in Indy (until TODAY!) and I hate for anyone to miss out on having fun with their smarts......especially a CABRIOLET!
btw, what kind of Nav does it have and is it 'user friendly'?