Re: Noisy squeaky back wheels, please help...
Could be a seizing piston or sticking pads.
Look at the pads first. Once the caliper has been displaced the pads should pull out very easily. If they don't, clean everything and try again. If they still don't, you may have to remove the paint off the end of the pads (if this is the problem). Lube carefully with copper ease grease on assembly.
If it's a piston, then one sneaky trick is to pump the piston until it's almost out, then clean it up with some fine Wet 'n Dry. Make sure everything is super clean, lube piston with clean hydraulic fluid and wind it back in. Saves bleading!