1999 gmc jimmy front passenger side grinding noise

The hum is probably a bad wheel bearing.

P304 is a cylinder misfire code.


P0304 GMC Cylinder 4 Misfire Detected

A full rotation and balance couldn't hurt. Possible brake issue too...

Sounds like front wheel bearings.
Does the sound go away when swaying one way or the other?
If you way left and ot gets louder it should be the right bearing and opposite for swaying right

switch the front tires left to right /right to left see if the noise gos to the drivers side if it does it is the tires put them on the rear and in time they will get better i have seen this countless times

you most likely have a bad axle. i would check the axle boots to see if they are ripped or if there is any play in them. also the vibration could be comming from the axle or a bad tie rod or ball joint

could be o2 sensor

-Drivers side starting at the front of engine: 1-3-5
-Passenger side starting at fornt of engine: 2-4-6

I have had the same problem with my Jimmy. While on a road trip in 2WD same as you, I slowed down for gas and same thing, nasty grinding. The problem is the collar that engages the front differential was grinding against the gear, eventually causing it to weld itself together. Putting the vehicle in 4WD takes the pressure off the fork which slides the collar over the gear. THE CAUSE OF THE PROBLEM is the air actuated switch on the transfer case, which is directly controlled by the switch on your dash. This switch gets hung up half way and causes the fork in the diff to move half way, which is where you get your grinding. Its incomplete meshing of the gears. The fork in the front diff is controlled by air from the air switch (or vacuum, lack of air, I cant remember) Take your jimmy to your local trans. and gear shop and have them check it out. The switch on the transfer case costed me $40 and replacing the bad gear and collar in the diff costed me $280. I did not have to rebuild the entire diff. Make sure you are not paying for parts you do not need. ask lots of questions!
Hope this didnt sound too complicated. By the way, I am also a fully certified truck transport mechanic.

Hope this helps.

Just had the same problem left front wheel bearing was gone in mine hope this helps should get it looked at rite away front wheel will seize and cause a lot of other damage

i will be honest u probably just need to have the front end serviced. could be the hubs and or bearings....transfercase