After I shut off my truck, about 5 to 10 seconds later it sounds like a compressor or small motor is running, and it runs for about a 50 to 60 seconds. It seems to do this even if i turn the ket on and off, sometimes. Can anyone tell me what this is. Thanks mayneman

 

Per Ford 2015 service DVD on operation of the DEF system

When the vehicle is shut down, the PCM closes the reductant injector and actuates the reductant pump purge valve, causing the reductant pump to reverse the pump flow and bleed down the pressure from the reductant pressure line. The PCM then opens the reductant injector to allow air to enter the reductant pressure line, which in turn allows the reductant pump to purge all remaining reductant from the system and return it to the reductant tank. The PCM then closes the reductant injector and returns the reductant pump purge valve to the forward pump position.

This is the noise you hear...

 

Yes, normal operation.