I'm still searching through threads trying to solve the problem, but I thought I'd go ahead and ask for help since I haven't found it yet.

97 F150 4x4 5.4 140,000 miles

I have a whistling type sound coming from under the hood that you can barely here when accelerating, but when going back down you can hear it very plainly. Thought it was the bearings on the alternator, so I put a new alternator and belt on. Still have the same problem. Thinking one of the other pullys maybe, but haven't got to check yet. Is there any certain one that would make that type of noise over the others?

Any other ideas or anything else to check?

Thanks in advance,
BT

 

serpentine belt maybe?

 

whoops didn't see you had changed the belt

 

check for a vacuum leak, a propane torch will show an increase in rpms when held close to the leak, ps don't lite the torch

 

I noticed my AC pulley was a little loose. Behind the triangular that the bolt holds one two thin pads. Are these supposed to be loose? I don't think so offhand, but I'm no expert by any means on this stuff. I can definately tell the noise is coming from the passenger side of the truck. If it's not the ac pulley or the tensioner pulley, I'm not sure what it could be besides a vacuum leak as mentioned above. Any help is always appreciated.

Thanks again,
BT

 

I noticed my AC pulley was a little loose. Behind the triangular that the bolt holds one two thin pads. Are these supposed to be loose? I don't think so offhand, but I'm no expert by any means on this stuff. I can definately tell the noise is coming from the passenger side of the truck. If it's not the ac pulley or the tensioner pulley, I'm not sure what it could be besides a vacuum leak as mentioned above. Any help is always appreciated.

Thanks again,
BT