Jeep Repair: engine noise, jeep grand cherokee, vacuum leaks

Question
Hi-
 I have some experience in auto repair and had my friend look at my jeep grand Cherokee as well, and we can't figure this out.
 There is a noise coming from the passenger side engine area, sounds like the hissing of a weedeater. The harder I accelerate the louder it gets. Then after I reach my desired speed it quiets, until I accelerate again. We checked for vacuum leaks and haven't found any. Also I don't have the power like I used to. Any help will be appreciated. Thanks.
                           BK

Answer
When I can't find a noise, I have a three foot section of garden hose I use, ear at one end holding it on various areas at the other.  I can usually pinpoint the problem pretty quickly.
A wild guess: your starter gear is not disengaging from the flywheel.