After I drive for a little while whenever I let off the gas there is a high pitched whistling noise. Once I push on the gas it goes away but comes back on once I let off the gas. When I stop driving it will whistle for awhile as it idles but it eventually will go away after a few minutes. It sounds like it is coming from the engine area. It is a 99 jeep grand Cherokee limited I6 4.0

 

vacuum leak. take some starting fluid or carb cleaner and spray you vacuum lines and around the intake manofold. mine was just doing this. ended up being the intake gasket. changed out the gasket noise is gone.

 

Is it anything serious that I HAVE to fix or can I just leave it alone n deal with the whistle noise?

 

i let it go for a couple of weeks but i think it got worst.i was tired of people looking at me funny. some people would ask what that noise was at first i would tell them it was the super charger. lol. didnt take to long to change

 

Ya it's been doing this over a year and hasn't gotten worse. I'll have to look into fixing it though...

 

Look and see if PO put a tb spacer on it

 

Does it start at like 30 MPH?

 

Hmmm maybe it usually happens after some highway driving n then when I let off the gas it whistles...

 

You know, with a vacuum leak, the PCM is compensating for the leaner mixture and delivering more fuel. This leak is apparently temp related and only shows up after the engine warms up. I would suspect intake manifold gasket or throttle body gasket. JMHO.

 

Is it something critical to fix?

 

I have this same thing going on in my xj. Quites as soon as i get out to look for it. keep us posted on what you find!

 

Ya that's exactly what happens to me I get to try find where it's coming from and goes away...

 

It's really annoying. Im gonna try the trottle body gasket for 5 bucks and about 10 minutes. I think if it were the intake gasket itd whistle when I press the gas not release the gas. who knows.

 

Ya I figured it was something to do with the throttle as well

 

On the WJ Grands when the wheel bearings go they make a high pitched noise at like 30, then the outer edge of your tires start to wear. Had this happen to two of my grands and my neighbors too.