loud bang! in the exhaust system?

86 bronco II. I changed the valve cover gaskets, sparkplugs, air, oil and fuel filter. Now there is a freqent bang noise that seems to be in the exhaust system. The car was not doing this prior to my repairs.

Is it backfiring? You changed the plugs? Make sure you got the right plug wire on the right plug. Double check you got the correct firing order.