I had the same problem. If you take off the door panel, look behind the speaker for ford's yellow box-like wiring harness. Well on my car, the window rolling down would hit the wiring harness and losen the connection to the speaker, I simply removed the harness and rewired the speaker. I could have just tucked the wiring harness underneath something in the door, but i was in there anyway so i decided to get rid of it. It fixed the problem and haven't had any troubles with it for 5 months.
