The large metal box part of your Air Conditioning system that sits outside is the condenser.
Don't turn on your Air Conditioning system when the outside temperature is below 65º F (16º C) or you may damage it. The life expectancy of a compressor is typically 10 to 15 years in moderate climates and as little as 8 to 10 years in hot climates.
It's important to make sure the condenser is on level ground (within roughly 10 degrees). You should also check to make sure that the condenser is positioned at least several feet away from exhaust discharge vents as it can affect the operation of air conditioning systems.
If your condenser is running loudly, a technician will be able to assess the problem and offer remediation advice. In fact, an anual system check is recommended to help ensure that everything is functioning normally.
Change your filter. You can usually find your filter in the ductwork near your furnace.
Keep your condenser clear of dirt and debris. As the fan draws in air through the coils, dirt outside your condenser can come inside reducing airflow through the coils, compromising function.