Weren't those a five year warranty? if the rear wheels turn freely, my first thought is that the transmission in seizing.

Drive control cable may need adjusting and/or the drive sector of each rear wheel may need cleaning and lube. Find the clamp on the handle that holds the engine/blade control and drive control cable housings. Loosen it and push or pull the drive cable housing - I never can remember which way it goes. What you want is about 1" of free play on the sliding handle that controls the drive. If that works and you get the proper drive control but it still squeals, it may be simply the rear wheels squeaking from lack of grease at the axle bolts/wheel hubs.
The drive sectors should be cleaned and greased yearly, including the hubs, wheel gears and ratcheting drive gears. Take off and do one wheel at a time so if you forget how the washers/spacers go back you can look at the other wheel assembly. Use mineral spirits and a toothbrush to clean with. The ends of the axle have a hole for injecting cleaner and grease into the drive gear assemblies. Try to clean grit out of the hole with a toothpick or pipe cleaner, then inject some kind of solvent spray with the straw on the nozzle. I like to use the spray White Lithium Grease which contains a solvent and leaves the grease behind when it evaporates.
After a few years of use, I also take a hand drill with a 1/8" bit and slowly drill a hole in the trans housing at a corner. The bit pulls the plastic cuttings out as you go, keeping them out of the trans. Then I fill it with Sten's #00 grease in the quart squeeze bottle with pointed spout. You could also use the spray grease with the straw in the nozzle. I finish this by putting a short self-tapping hex-head in the hole.