hey i have a 99 w/ a 4.0, and during the summer when its real hot my engine makes a real loud low pitch whistling noise. my 96 that i had before this one, which also had the 4.0, did the same thing. i have a k&n on it, but i dont think that it is causing it because it did it before i put the filter on too. the noise can be heard the loudest coming out of the filter. any one have the same problem or know what it is?

I had the same problem with my 96. It made it after I put an intake on it, then stopped after I put the stock one back on. (I know not really that helpfull)

Kinda like a loud vacuum right?

yeah thats what it sounds like, but mine did it before i put the intake on it also. and i talked to some random person that saw me lookin at it while it was makin the noise and she said that she used to have a stock ranger that did the same thing. weird...

Yeah now that you mention it I think mine did to, but the intake just made it worse lol