engine noises

While going up a steep hill at about 45 mph yesterday I heard a noise that I thought could be in my driveshaft, but I sat in my driveway and revved the engine up and the noise was there in park and neutral from about 2500 rpm to just under 3000 rpm. This won't translate well, but it was of the "waaaawaaaawaaaa" variety. With peaks about every 3/4 of a second. Does anyone know what this is? '99 XJ with AW4, NP231 and 130K.

Noises can be difficult to troubleshoot online. You'll need to put in your time to try to isolate it. Is it coming from the engine bay? If it's in the engine bay, then I'd concentrate on all components in the route of the serp. belt. including the belt itself to start with. Do you have a mechanics stethoscope? They can be really helpful in tracking down phantom noises.

If you could get a hold of a video camera and record the noise along with commentary and post it on Youtube with a link, that has been very helpful in the past.