Air comp. Q

[timgco]

I was airing up my tires in the driveway (it pitches down to the street and I was backed onto it) and all of the sudden I noticed my truck squating. The tires were completely in the wheele wells. After I was done I went for a ride around the block and it cam back up most of the way. It's going in for servie for other things, but this was a first for me. Anyone else have this happen?