i have had my 06 150 for about 3 or 4 months now and love it!! but the other day when i started it, it sounded weird so i revved it up a bit and when the RPMS were coming back down it sounds like its back firing but it sounds like tin... only does it wen it cold tho.. is it something in the muffler?

 

check to see if the skid plate that runs from side to side that shields the transmission isnt slightly touching the exhaust pipe right after the cat on the passenger side. its the small (maybe 12'' long x truck width) that is even with the doors and its held on with 4 bolts.

mine was doing that and i took a grinder to it and solved my problem. it was a very loud metal rattling sound.

 

i will have to check that out thanks!!!

 

it IS a backfire and its normal. the tin sound your hearing is the baffles in the factory muffler. if you had aftermarket exhaust you would hear it more. keep in mind when you first start your vehicle it will run very rich in open loop. reving it up will cause backfires from excessive fuel in the exhaust.

 

ok cool thanks!!