Hey KingMike, The 5th. generation 78-87 always had a heavy 'close-door' sound. Also close both doors, each sound will be a little different. Try opening the pass. window & close the driver's door, then close the window, try again & compare. The only other thing (aside from above advice), is check the latch catch bolt on the body side. Look for metal on metal marks; lube the latch & catch bolt with grease and close it again, see if different. Both of my doors 'boom' when closed too. - George