I am new to this site but not to jeeps my family has owned them since they first downsized and with 502k on my previous 91 xj navy coupe 5spd without any major work im a believer

a few years ago i bought a 98 xj 4x4 auto and its been a good car (not as good as the 91) but i digress it started humming/light vibrations today with engine rpm speed and i cant seem to find it i think its the trans but it sounds and feels closer to the engine but i can her the trans down shift now becuase of the humm its not the wheel bearings or u loints because itl do it in park i looked for any rubbing parts and nothing and sprayed some lube on the pulleys to see if its a dirty bushing

it dosnt do it loud at idle but a little above idle it gets louder then at about 2500 it starts to quiet and go away

 

loosen serp belt and spin all pulley see if one harder to spin than others .

 

My alternator started doing that when the bearings started to go bad. Then it got way worse and was unbearable! But definitely check your pulleys and then go from there

 

found out the hard way a diode went bad in the alternator i just changed in January well at least it wasnt 12* outside for this one (that was ruff)