Grating noise in 2WD

Hi all, 

I have for a while had a brief grating noise in 2WD once I’ve hit 30mph or so. My initial assumption was a poor vacuum so I would just try again and usually it would ‘disengage’ the 4WD and the grating would stop once back in 2WD. However recently the grating noise has not stopped (when in 2WD) from the nearside front wheel of my 2007. 

I initially changed my Diff oil, however this wouldn’t be a problem as the front diff isn’t doing anything in 2WD. 

I have taken the hub cap off and it is 100% disengaged. I have also driven with the hub cap off and the noise remains. 

I have done an idiot check to ensure no debris is around, however this couldn’t cause anything as if there was, it would grate all the time! not just in 2WD. 

For this same reason I would assume it is not a bearing issue, as surely it would grate all the time, and not disappear when in 4WD, however I do not fully understand this part of the car. I have read:    
www.bigjimny.com/mediawiki/index.php/Fro..._bearing_replacement to get a better idea but my quiery remains. 

Anyone have any ideas why this grating noise disappears when in 4WD?

A common cause is a leaking vacuum solenoid. This will mean the hub is gently being pulled into the lock position, against the splined engagement ring.
The solenoids are beneath the battery. There are 2, one for lock and one for unlock. You could try swapping them around and seeing if the problem persists. They are straightforward to disassemble and clean.

Thanks for this, will give it a go.

Upon further thought, if this was the case then the noise would go when driving with the hub cap removed, would it not?

Crazy as it sounds (no pun intended) check the other side as well.

Sounds travel oddly, I once spent weeks chasing a noise from the back axle that turned out to be a front wheel bearing...

Also have a look for debris/nails in the tyres.