I have a 1994 f150 XL 4x4 4.9l L6 5 speed One day at a stop light i noticed a slight whistling. it quickly grew into a high pitched whistle that cut in and out while idling reviving the engine dose not make it louder or quieter its very random but really noticeable even over the engine noise at some times it even drowns out the engine entirely. it seems to be coming from the upper halve of the engine closer to the front. i think its the belt but not sure as it is to loud to pinpoint exactly. Any ideas on what it is? Id bring it to a shop but I'm a college student and well cash is for the working LOL I have ruled out the vaccum hose,air intake,exhaust manafold,exhaust,and the fan clutch.It almost sounds like metal on metal but its very steady.?????

 

Sounds like it might be a ball bearing, A/C, altenator, water pump, idler pulley. Use a long 3/8th extension, touch it to and area where you think the noise is coming from and put your ear on it. You will definetly find out where it is coming from then.

 

thank you I will try that today! thank you!