I have a 2013 Silverado Z71 4 door. Recently I noticed that after it rains there is water inside the rear passenger door, can't see any holes or where water can get thru the moulding. Any ideas

 

Had the exact same problem with mine. I took it to the dealer and they sent me to the body shop. There is a drain plug in the bottom of the door that was clogged up. 5 minute fix after removing mouding to unclog the drain hole. No issues since.