Bed rattle FOUND

Been fighting a rattle in the rear of truck for months. 20 Pro. Found the front bed bolt pass.was tight but with slack enough that I can wiggle the front of the bed and see the slack and hear the noise. I don't have a met. torx that large to turn but with a metric allen it would not turn.
Questions, why? what size is the head and was there a spacer or fiber washer on the bottom side that broke away? Is the nut attached to the frame or am I going to have to have someone under to back up the nut? Never had the bed off before. Only 45000 on truck and I'm sure the warrenty isgone for this.
Thanks for any help.

 

Home Despot carries the giant torx bits. Can't remember what size.

 

It’s a # T55 I think. I know this because I had to loosen mine to adjust and straighten the bed alignment.

 

I got a great deal on my truck because of this exact rattle. Dealer couldn't solve it so I saved a couple grand. With heavy off roading or the carrying of heavy loads the composite bed will rub on the frame of the truck and start to wear away. This causes the bed to get loose and rattle. The answer isn't to tighten from above but instead shim from below to prevent the rubbing. Loosen the bolt, lift the bed a bit and shim it up between the frame and the bed. I used a bit of rubber from an old motorcycle tire tube and intended to replace it with something a little more durable, but it's been over a year and the fix is still working so I haven't messed with it.

Before you loosen the bolt check to see if you can create a gap between the frame and the bed by having someone lift up on the bed while you look at the bed mount underneath:



Once you loosen the bolt you should see the metal sleeve sticking up. This sleeve is there to prevent over tightening of the bolt so the bed material doesn't crack. You need to shim the bed up so it's even with the top of that sleeve:



Here's the rubber inner tube I cut, doubled over and inserted around the metal sleeve to shim up the bed:

 

Great reply! Thanks

 

Warranty?