Upon moving from park to drive when first starting, my 2002 PT Cruiser jerks a little and seems to not go into gear. What could it be?

Only when putting it in gear from Park to Drive does this happen and it seems only when first starting. It is fine while driving and also fine when going from Park to Reverse. But when going into Drive from Park when I first start it in the morning, it does not immediately go into gear, idles a little, then kicks in but with a strange 'bumping' sound that seems to come from the back. The gear shift (automatic) does not feel sticky and feels normal.