Aren't the door locks vacuum? So they would not cause the problem.
The motor noise might have been your antenna, which has an always-on connection to the battery so it can retract when you turn the ignition off. Try disconnecting it.
You might also check if your trunk lid is closing enough to turn the light off. I removed the bulb and my problem went away, although I need to figure out why it is happening. Believe it is a worn latch.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe