Unusual for a gas engine to knock like a diesel. You don't state its
mileage so we have no guide to the engine's wear. Knocks are usually
from pistons or bearings. A valve lifter will tick, the timing chain
rattles; the deeper the knocking sound the less you will want to hear it.
Could it be related to the drive belts?
Why are you running the engine if the car is in storage?
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