Problems with check air suspension light coming on?
That creaking sound you're hearing is the car raising up when the air compressor kicks in to pump air into the system.There's probably a leak somewhere.Depending on what's wrong these systems can be real expensive to fix or replace.You may have to go to an aftermarket suspension setup.I suggest checking out either Sun Core Ind. or Strutmasters.They both make suspension systems for Lincolns and Cadillacs.
The air suspension is controlled by a level sensor that is connected to the rear axle by some linkage. That sensor should be checked for proper operation first. If that checks out, then you might have a problem with the circuitry going from the sensor to the compressor motor or the compressor itself is bad. Worst case scenario is the air bags are bad and they are very expensive to replace. If that is the case, I have heard of companies making strut kits to install in place of bad air bags. It might not be an original fix, but it is a far cheaper alternative.
This happened to another technician at the Ford dealer. I think your car has air suspension on all four wheels. I also think they are complicated system. The tech at our Ford dealer had a hard time with it. I don't know personally as I have never done one. Just trying to help.