What causes clunking sound when shifting from park to reverse on 2006 Hyundai Sonata

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The vehicle has a 5-speed automatic transmission. When shifting out of park to reverse the engine makes a loud clunk sound and a brief grinding noise once the vehicle starts to move backwards. upon shifting into Drive there is no more noice to hear. This only happens when the engine is started being completely cold. No clunk or grinding noise can be heard when shifting out of Park into Reverse once the engine is warmed up.
(1) Answer
Park in the opposite direction so in the morning you are taking off in drive and see if it does it then.
Do not shift to reverse at that time, just put it in drive and go. Then post the results. Or not but i think we may have an answer.