Turned out to the be the aftermarket exhaust tapping on a heat shield.

 

Is there a car seat point and clip behind there? Jack assembly not secure? Best bet would be to fold your seat back down and check.

 

While you are searching for your noise, take a look between your cab and bed - sometimes a stick or something can get lodged in there and cause a noise.

 

I just bought my 10' and its doing th same thing, its annoying the hell out of me!! I havent had a chance to source the source the problem yet... Ill let ya know if i find it

 

Yeah I have had sticks, large acorns, etc. get stuck between bed and cab that annoyed the hell out of me until I found them.

 

I looked yesterday. I opened the passenger rear pillar to see if anything was in it that could rattle. Nothing. I couldn't figure out (with my lack of patience) how to get the back seat off.. so that's where my journey ended. I DID get into the JACK ASSEMBLY and put a torn up towel under it to keep it from moving, but the rattle persists. I'll check between bed & cab today, but I don't that is it.

I checked the child safety loops, but they don't seem to have anything that could rattle.

OXFX4 please keep me in the loop if you find anything!!

Kev

 

I have the same thing. Mine sounds like plastic rattling on hallow metal or something along those lines. It only does it at low speeds over uneven or bumpy roads. I am thinking of ordering some more Fat Mat rattle trap.
http://www.fatmat.com/
I bought the door kit and put it under all my door panels. It made a HUGE difference in the noise comming into the cab. My next project will be to put fatmat under the headliner and behind that c-pillar. I will also put some foam cushioning on the edges of the c-pillars to keep them from rattling on the back of the cab.
The only place I think it can be coming from is where the c-pillar cover hits the metal by the back window. I hope this helps yall!

 

Dang! Nice.. let's get this annoyance resolved, sounds like we have the brain power, now we just need the hands-on resolution.. anyone?? anyone??

 

I've owned two 2004's, a 2007, and now a 2010 King Ranch and all of them had the rear window rattle. After tons of research and back & forth with two dealers on the first truck, they finally found a TSB for it. The dealer didn't seem that happy about fixing it but finally admitted they needed to keep the truck for a while to fix it right. They had to remove the rear window & do something with the mounting or seal around it. Sounded like the actual window rattles in whatever mounting it's in. After the dealer performed the fix on all 3 of my previous rigs, it completely went away for the remainder of the time I owned them. My '10 KR just started doing it after 14K miles & it's "here we go again" time at the dealer next week to convince them it's a known issue & they need to fix it under warranty. If yours is the same as mine, it's definitely not a seatbelt, seat or jack issue. It's definitely in the rear window. Give em hell at the dealership & hopefully they fix it for you. Good luck guys.

 

Wow Really!?!?! I'll run this by my local rep.

 

Yep. It literally got to be embarrassing. Here I had this brand new nice truck (especially the new KR!), and I have to explain to people what that ridiculous rattle is behind their heads. I can't believe it's still an issue & they haven't resolved it at the factory even with a brand new redesign. Don't get me wrong, I've loved every one of these I've owned, but when it started last week I just shook my head. The dealer of course tried everything to fix it on the first one until they finally agreed to pull the window. Luckily on the second & third it was the same service manager & he didn't ask twice when I showed up less than happy to see him. Interestingly all of mine were on what sounds like the driver's side, but maybe that's just because that's where we're sitting. Hopefully this'll save everyone some back & forth time with your dealers if this is what you've got. Can't wait to go in this week & see how much convincing it takes since it's a new dealership...

 

I had this same rattling in my 2010 F150 SCrew Lariat. My husband thought it was the rear window, I thought maybe something with the seat. Dealer found that some clip in headliner was broken and loose, therefore rattling over bumps. They have ordered a new headliner to install next week. On my way home I tested it out with current headliner - over bumps I pushed on headliner and I didn't hear the rattle and if I bang on it with my hand I can make a similar sound. Maybe this is your problem too.

 

My rear window rattles too especially when shutting the doors. Annoying, yes, but that sound seems different than the plastic tapping sound you described. The rear window rattle sounds more like a heavy piece of glass up on its side hitting something solid. Go figure right? lol... more of a thud. Or atleast it is in my truck.

 

well just a thought... 2010 screw cab, the plastic filler funnel rolls around under the drivers side back seat.

 

that "should" be clipped in to the tray in that whole... although mine was ditched to mount my amp there lol.