First off i know that the 00-01 xjs have the two peice manifold that I guess can NEVER crack.. I had a 99 about 5 years ago that had a horrible crack in the manifold alomst in two peices!!! I can remember the horrible noise the 99 made and its a simmilar noise just not as loud.. its almost like one of my exhaust valves isnt opening enough?? i have no idea.. my sisters 2000 xj has the same noise but its more rappid and not as noticable.. the noise isnt really loud unless you listen for it.. its a hissing but in a rythem, hisss hisss hiss hisss.. this only happens around 1700-2200 rpms.. my sister bought her jeep new in 2000 and i dont remmber her jeep having this noise new... its hard to explain but i know someone out there has some GOOD input or is in the same situation as me... I really appreciate the replys, glen..

 

bump.. need to figure this out its driving me crazy...!!!

 

does it happen when the engine is cold and/or warm?

 

thanks for the reply.its a all time noise.. warm cold hot watever its there.. i am stumped!!!! cant figure this out for the life of me.. its been on going since about 50k... thanks again for the reply..

 

hmm thats really strange. I had somewhat of a similar sound but it was the manifold and only when it was cold.... i know a ton of cherokees including mine have loud lifters but that doesnt really sound like its that. you sure its the exhaust?

 

are you positive its from the exhaust or somewhere in the engine? like a lifter or something. you can run some seafoam through the TB to help check for leaks in the exhaust system.

 

go under and inspect the pipes , if it has leak youll hear it better. my 95 had a 3/4 crack around the lower pipe of the manifold. i took it off and welded it back together , leak is gone.

 

damn lots of post, thanks guys... I doubt its the manifold.. 00-01 cherokees have a cast iron 2 peice exhaust manifold, suppose to be a better crack proff design.. maybe im the first to find this flaw out!!! Over the course of 4 years i have noticed a slight hissing.. Its gotton faster ond a little louder..its not noticable unless you are paying attention.. with the windows down and going by a building or parked cars its more noticable.. My sisters is the SAME!! 2000 cherokee with the same noise just in a faster rythem.. hers is also really loud at idle.. sounds almost like my 99 xj witha cracked manifold.. I replaced the manifold 's gasket and did not see any cracks in the exaust manifold.. i am starting to think its a valve-train issue.. thanks agian guys, your input is appreciated.. GLEN

 

open your passenger door and listen near the floor board. See if it is any louder in that area. I have a similar noise seems to be coming from under the floor around were the bulge for the transmission is. I thought it was an exhaust leak but I had everything checked out and its all fine. If this is the same noise you have, good luck figuring out what it is. but if you do please let me know.

 

I Could find a freind to drive my jeep so i could lean out the door and listen, sounds like a rush haha.. you have a simmilar issue?? explain your noise a little.??

 

Haha, that would be crazy. no i mean while your truck is running but Stopped! Lean in from the outside and listen. the noise I have is very faint at idle but you can hear it if you listen for it. Its like a hissing or a tapping that speeds up and getts louder with RPM. I beleive it goes away about 2500 or so. Or maybe the engine noise is just to loud to hear it after that. I know that I can drown mine out by turning the radio up a little but its just the point that I know its there and I cant figure out what it is.

 

sounds to me like the same noise.. YOu can hear the hissing at idle?? or are you reving the engine up??? i am sure i can only hear mine under accel or load.... i will check today.. its not that loud though... if you are REALLY paying attention you can hear it.. nobody has noticed it though besides me.. the hissing is getting a faster rythem and a LITTLE louder.. more noticable when going thru a parking building or somewhere with walls...or going by parked cars on the side of the road.. I will check today at idle and see what i got..thanks for the replys man i really appreciate it...

 

yeah, i can hear mine at idle but its very faint and i have to be listening for it. I cant hear it very much out side though. the only place i can hear mine from outside is when I put my ear up the the cow (under the winsheild wipers) on the passengerside and I can hear it through there. Ive looked all over and it drives me crazy.

 

Check the connection at the 2 peice. The donut gasket might be bad.

 

PURGE SELENOID... I am thinkg that s what YOUR hearing.. if its on the passenger side anyways.. check it.. it by the a/c lines and should be bolted to the engine bay.. it sould make a hissing or ticking.. maybe this is your problem.. Idk a wild guess...