If you hear a thumping noise coming from your attic, it is likely an issue with your attic fan. Used to ventilate the attic, and in some cases the entire house, a problem attic fan often creates a thumping sound. If you are using an incorrect size fan, it can cause the motor to work overtime to function properly, leading to a thumping noise. Attic fans with loose parts can also cause thumping. Regular maintenance, such as lubrication and tightening of parts, can prevent the thumping.
Your attic may make popping noises, especially after a large drop in temperature. The wood and other materials in the attic absorb heat and can quickly lose it if temperatures plummet. The popping noises come from this heat being lost and is completely normal. If you do hear popping noises, don't ignore them. They could also be coming from an animal infestation or damage occurring in your roof. If the noises continue after thorough inspection, you can assume it's something benign.
If you hear scratching noises in your attic, especially at night, it can be a signal that an animal or animals have taken up residence there. Anything from rats to birds to raccoons can move into your attic, since it is an enclosed space that can protect them from the elements. Rodents such as rats and mice can chew through insulation and build nests in your walls while larger animals can enter through loose screens. If you believe your attic is infested, contact an animal control professional.
A "settling" house can also be the cause of noises coming from your attic. Anything from thuds and groans to snaps and cracks can be a result of this phenomenon, especially if your house is a new one. Settling can also occur after an earthquake or during periods of heavy rainfall or drought. Settling is often not a cause for concern, but keep an eye out for cracks or other new damage.