Recently picked up a '98 F150, 4x4 Supercab XLT, 5.4, 116k miles. For some reason, it has an extremely high pitched whistling noise (like a dog whistle)that is loudest at about 22-2500 RPM. it has the same tone/sound as brake wear indicators almost. Makes the noise only with RPM. Does not matter if stopped or moving, in or out of gear. Very strange. Unfortunately, I am not too familiar with this 5.4 motor and have no idea what to look for.

Anyone ever experienced anything like this? I searched the forum unsuccessfully...

thanks in advance,
John

 

does it happen to have a throttle body spacer? they are notorious for doing nothing but whistling.

if not i would say vacuum leak

 

Or an idler bearing going out.

 

is that the bearing on the pulley for the serp belt idler, or something different? Thx for the response.

it does sound like more of a bearing noise than anything else. no TB spacer on this one, anyway.

 

I Have the same year/engine, one of my idlers is making that noise, but not that loud, almost not noticeable.