Need help with vibration

So this past weekend with the snow is the first time I've used 4wd in my truck, just used 4hi not 4lo. Snow has cleared and roads are dry but my truck has a vibration between 30 and 45 mph that I feel in the floor board and the foot rest. It feels like it is coming from the front end and also when braking in that speed. Weird thing is I put it back in 4wd and don't feel it. Also note that when I drive the truck 10 miles or so it goes away. I washed the under carriage of the truck thinking it may of been a ice salt build up but didn't solve it and also check the lug nuts to make sure they were tight. anyone have any input on this before I take it to the dealer? truck is still under warranty.

 

Any snow/ice on the inner side of your wheels? That will cause an out of balance condition.

 

nah I thought the same thing but I washed everything out underneath including the wheels but the feeling does feel like a out of balance wheel but I didn't hit anything or do anything to throw a wheel out of balance.

 

It still could have thrown a wheel weight...