This sounds like tire blooming.
Tire rubber usually contain an anti-ozonant which prevents UV damage to the tire (like you might see on a windshield wiper blade, it starts cracking). The anti-ozonant, when exposed to air, turns brown. Since the anti-ozonant is part of the tire's rubber, it continues to rise to the surface of the tire.
is it possible to get rid of them?
Usually you want to use a gentle cleaner. Using something too harsh may result in exposing more the the anti-ozonant to the air. Once it's cleaned off, dress the tire in a protectant.
is this something I could take up with the manufacturer to get them replaced?
Perhaps. If it is tire blooming then might tell you its completely normal and expected. It might be the result of a manufacturing issue, returning "within hours" is a bit unusual, I would at least make an inquiry to the manufacturer.