Last Dec I took a road trip with my Tele and Strat in their cases. When I got home I noticed the strings were higher off the frets. The neck looked bowed up. I adjusted the truss rod a bit till thing looked straight. The action still was a bit high I got thinking about the change and checked out the screws. Should had done that first. The 2 bottom screws were not even firm. The top outer screw was semi-firm. The inner was good. I checked the strat and it was the same. Both bottom not firm and the same for the top screws. Now the other day I again found one guitar that the screws backed off again. The Stratocaster I got 4 months ago. I checked all nuts, screws and knobs when I got it. Am I putting force on the neck causing this? Would seem the tops would loosen first. Truss rod do this? I never touched it before this last Dec. I've worked on cars most my life. I think I have a good idea what firm is as opposed to over-tightening/stripping. I used great force this time when I tightened the screws making sure they were tight. Any ideas? The room temp stays fairly constant. I run an air purifier that contains a humidifier. Stays 45- 50% in the room. Maybe it's poltergeist? Or is this a common maintenance issue?