I have a 1991 Jeep Wrangler that has about 115000 miles and quite a bit of wear and tear. This problem is that about five minutes after I have started to drive my jeep, it makes a whistling sound almost like a supercharger or a turbo. This noise only occurs when I am driving at around 35mph to 45mph. If I hold a steady speed of 40mph the noise starts very softly then builds up to a very loud noise. If I give it more gas or let off the gas the noise softens but does not disapear. After some time goes by it may stop but it soon returns. What is going on?

If the noise is from the tail pipe you have a stopped up catalitic convertor.
If the noise is from the front you have a loose belt, or a bad bearing driven by the belt.
If the noise is from UNDER the vehicle you have a bad U-joint or throw out bearing...
If the noise comes from one side or the other you have need of new brakes! Be more specific! Where does the noise come from?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

i have a similar noise and i figure it is the leading edge of the hardtop. you may also check your stereo system. if you have much of anything besides the stock setup, the distributor and wires can interfere with your sound and can come through the speakers.

also i have a cheap aftermarket intake that whistles and annoys the shite out of me.