My wife got a '99 expedition, and when it gets shut off the compressor for the suspension runs very loud for a little while. It is also sometimes fairly loud on start up. Is this normal? any ideas what could be wrong?

 

Well the compressor on start up is normal. Depending on the temp outside the compressor can be noisey sometimes. When you shut it off though the compressor should go off almost immediately. Ours sometimes will come on when we back into the driveway due to an incline but it will shut off when the truck is turned off due to the fact that it is supposed to settle down an inch from ride height. I would say there is a good chance that you have a leak. Why not turn the suspension off when your wife gets home and leave it overnight. If the truck looks way to low in the morning then you do have a leak. Good luck