Have this unit looked at. There is no reason for the noise level to be more than that of the air movement. Yours clearly has something hitting something else. The old reciprocating compressors made noise but the new rotary compressors are quite quite. If you said the unit made noise after several hours of operation I would assume it was low on gas and freezing up and the ice hitting the fan.
Noise from the offset the fan assembly is the most likely one to create noise.
Before you change out the unit for a larger on consider what you want the unit to do. Most people thing bigger is better. Not the case with AC. An AC unit has to functions cooling and dehumidification. Dehumidification takes much longer and thus requires a longer duty cycle. If you oversize an AC unit you will have short cycling with rapid cooling but very little if any dehumidification. Trust me you will be much more comfortable with the unit running longer, and dehumidifying, even if at a slightly high ambient temperature.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles