A hissing sound coming from the power steering pump.

Well this morning I noticed my engine making a hissing sound and it would get more noticable under heavy acceleration. Took it to a shop and had them check it out with a stethoscope (luckily this was free) and their guess was that it sounded like a vacuum leak but they couldn't trace down the source. I was thinking maybe a cracked manifold but they didn't find anything near that. Couldn't really find anything until they took the cap off of the power steering. It let out its pressure and the hissing stopped. I noticed that the fluid level was much higher than it should be but I don't ever recall adding anything to it. So I took it back home, cleaned the cap of all the gunk and removed some of the power steering fluid to get it to its normal level. I was thinking this was it so after I was done I drove it around and the hissing returned. Got it up to 50 and accelerated hard a bit and I could really hear it just like before. Got back, popped the hood, took the cap off of the power steering and the hissing stopped.

Does anyone have an idea on what's going on here?

It's a '97 4.0L

Well, I took it back to the mechanic and had 2 people listen to it and they couldn't identify it or say why. Pretty much the consensus on it is that it's just a sound my power steering pump is now making or a exhaust leak that is just forming but that wasn't likely since they couldn't find it with the stethoscope or see a crack. Plus I seafoamed it yesterday and didn't notice anything. Sooo, I'm just gonna keep an eye on it to see if anything changes, otherwise, it seems like it's just another sound for my Jeep to make.

If anyone has anything to say, please, don't be afraid to.

This is interesting...I JUST did a Seafoam treatment and am having the same hissing sound. It sounds like it is coming from the power steering on mine as well. I know it has to be a vacuum leak. My idle also jumps to about 1100 RMS to now. Wierd.

(As you can see from my previous posts, I had just fixed the vaccum leak I created earlier when I incorrectly installed my intake manifold. Now I have this darn problem.)

Any ideas? (Mines a '99 4.0)