Grinding noise from front end
 

I recently bought a 05 f150 5.4 lariat 4x4. The other day I noticed a slight grinding noise coming from the front end. it doesn't make any noise driving straight but as soon as I turn a little left or right it starts up. It doesn't sound like wheel bearings and doesn't seem to be getting any worse. the tranny slips every now and then so I don't know if this could have anything to do with it. any ideas?

Check it for a vacuum leak. If it's happening turning both ways your hubs might be locked into 4x4. Easy check, get it up on jack stands all around and put it in drive and see if they all start spinning. But still do that vacuum test.