Central Air working fine. Last night I heard a loud rouring sound from the a/c when it was not running. Then I heard it again after it ran for a while. Every thing seem to be running OK. This sound occurred frequently but when the a/c is not running. May be coming from the ducts ? This is the first time any problems in six years. Also A/C is not connected to furnace cause I have electric heat.

Is the noise inside the house or outside?

The noise is inside the house.

The noise is inside the house. May be coming from attic area where the
Equipment is located.