Seeing that everything feels tight, I would be suprised if its a noice coming from the bearings/freewheel, though it definitely is possible. Do you have a spoke protector on the wheel? Its basically a plastic plate that sits behind the freewheel so if the chain falls off the largest cog of the freewheel it won't guage the spokes. These things are often a big culprit of annoying scraping noises.

Also, a good idea is to spin the rear wheel and while its spinning, try and locate with your ear where the noise is coming from. This will help you determine if its possibly a scraping fro the tire on the frame or cable, the rim on the brake pad, or from the hub area of the wheel.

Like suggested earlier, you'll probably save a dollar or two if you bring the wheel in to the shop with it off of the bike. However, it would probably be good to have the rest of the bike in the car. In case they don't detect any noises coming from the wheel by itself, you can grab the frame and have them put the wheel on and then diagnose it.