My 2008 4.6L is making a hissing sound when I excelerate and when I hold steady at 40-50 mph. It does it all the time but only at those times. What is it and can I fix it or have it fixed? the motor only has 12,000 on it.

 

did it recently start? or has it always done it? how noticeable is it? do you have an aftermarket cold air intake? maybe a small exhaust leak.

 

It has started in the last couple of weeks. Ppl in the truck ask whats that noise. The only thing that I have under there is a K&N drop in filter. It only does it when in drive sounds fine when im in park and rev it up.

 

You are on warranty - address this concern with the dealer.