I have a '08 F150 4.6 4wd, 72k miles. When pressing on the accelerator I hear a barely audible whine, when I let off it goes away. Sometimes it's there, sometimes not, mostly it is. I've replaced the tranny, transfer case and rear diff fluid but not the front diff. New air filter doesn't work. It sounds to me like it's coming from the engine compartment but I cant find it. It's been going on for about 15k miles and hasnt worsened. It's my work truck so I can't afford down time.
REALLY appreciate any help. This truck is my paycheck.

 

I don't know how bad it is, but I have read on here that the alternator bearing is suspect on these trucks.
on another thread;

And has the whine been there from the beginning? This is a known issue with the 2004 thru 2008 trucks. I have a 2005 I bought in 2008 with 22,000 miles on it and it's done this from the beginning. Only happens in air temperature around 32 degrees and below, and the noise comes and goes as you drive. Gets worse the colder it gets. I know some people believe it's the alternator and they have replaced them and the noise goes away. I've never had a problem with the truck it's just annoying. I didn't think your generation of truck experienced the problem though.

https://www.f150forum.com/f4/noise-2006-f150-xlt-73622/

A mechanics stethoscope would localize it.

Oh, leave the wife home. (just kidding)

 

Wow, I just got a new exhaust put on my truck on monday. Ive been listening closely to the truck and Ive noticed the same sound you're describing. I was really curious as to what this is as well. I have an 06 with 108k miles fyi.

I actually just had my mechanic buddy look at it. He said its just from the power steering pump. He said its just naturally loud, but there is no problem. Hopefully he's right.

 

Thanks. I'll defenitley take a look at that.

 

I also have the faint whine! 05 Screw 90k miles only seems to do it when its cold 32deg or colder. I only hear it at hwy speeds 50,60,70mph. Weird part is with cruise set at 60 its there 62mph, nothing, 59mph, nothing. Thought maybe a bearing in tranny , but that really dont make sense due to minimal speed change eliminates noise. Pulley bearings seem more likely, but idk.

 

At 1200 plus rpm in drive at any speed I start hearing a bad bearing like loose metal and I too have been supecting my alternator, it doesnt get worse or better if I give it gas but no whining its just annoying 07 screw

 

but I'm sure the stethescope from my sister inlaws closet wouldn't find it anyway.
I'm going to have my trusted mechanic put it on the lift and find it. If he cant find it I'll pay Ford a billion to find it.

 

Good luck! Ingleside huh? good fishin down there

 

I live in S Texas, the temp barely ever dips below 50F. The truck has that whine regardless of temp.

 

Awesome fishing, reds, reds, and more reds all day. Come visit, you'll leave mith more fish than you can eat.