The foam seal on the tray that holds the air filter was falling apart on my truck. I even have pieces that have come off and are caught in the air filter. I peeled off what was left and used some weather striping from home depot to replace it. Should this stuff have dried out and fell apart only after 4 years ? Just wondered if anyone one else has noticed this with their trucks.

 

Mine did the same thing and thats just what i did too

 

I know this is a old thread, but everyone with a 04-08 5.4 should pop the clamps and pull their air filter tray out and see if the foam seal is still around the sides and bottom of the tray. Mine was completely gone except for the adhesive strip that once held the foam in place. If your foam is missing, that is where the "drone" sound is coming from when you are driving down the highway and accelerate. Go to Lowes or Home Depot and buy a roll of the 1/2" wide by 3/8" thick adhesive back foam weather stripping and cut it to fit where the old foam was. I also put a strip across the top for a complete seal. Truck sounds 100% better and now ALL the air goes through the filter instead of unfiltered air going around it.