I have more questions, about the sound coming from 4x4 gear box I think.
When accelerating, there's normal engine sound and no other sound noticeable, but as soon as I remove my foot from accelerator mostly in 3rd or 4th gear, or press clutch there's pretty noticeable sound change. Sound goes from zeeennnn... to zooooonnnnn, and it's louder than engine sound. It's not the engine sound for sure, because the foot is off the accelerator.
Yesterday, I removed one of the rear wheels, and tried to spin it's base by hand, it also made the rear drive-shaft spin. Even though jeep was set to 2H mode. So, rear wheels are always engaged. front wheels engage when vehicle is set in 4x4 mode. The sound is definitely coming from the small gear box, i.e. which handles the 2H, 4H, 4L modes, where the rear drive-shaft was connected and I noticed the small gear liver to switch modes is also comes out from this gear box.
So, my question, is it normal? Does it suppose to sound like that when gear is idle in high speed (40-50 KM/h)?
Also, I removed one of the front wheels as well, and noticed that I cannot spin the base easily, break shoe is gripping disk too tight. I think this is not normal, wheel should spin free when break is not pressed. This could be the reason I'm getting about 8km/l average. I will take the car to mechanic on weekend and get the breaks serviced.
Edit:
There's one more thing, the rear wheels are smaller size than front wheels. Front wheel are correct size which label says on the driver's seat door 175/80 R15. The rear ones are 195/65 R15. This could be the reason too for gear box sound, as the smaller wheels need to spin faster than front wheels, impacting the overall performance too.