The bolts/nuts holding your rear motor mounts could also be loose. I think I'd check them. You might also (a) tell your wife/girlfriend you've cancelled any life insurance you have and have altered your will to give all your worldly possessions to me (you don't have to actually do this...just announce you have) and then (b) slide under the truck while she races the engine to see if it is lifting off of the rear mounts. Then later after a glass of wine or beer, tell her you were just kidding...and prepare for the temperature in that room to fall by 5 or 10 degrees.
