drove it to work this morning just fine. turned it off no noise. drove it from my work to the gym. turn it off and i get a noise sounding like a dying horn. weird start it back up, shut it down get the same noise. drive it from the gym to the store, again with the noise on shut down. drove it home from the store and when i get home same noise. no clue. truck ran fine the entire time. no warning light, nothing other than the noise. its quick only makes noise for a second and the closest i can get to describing it is a dying horn or weezing sound. im stumped.

 

Could it be a radiator cap?

 

i dont know kinda sounds like its coming from somewhere inside the cab

 

I've heard of people saying the 4 wheel ABS module can make noise after the engine is turned off.

 

Put a pressure tester on the cap and the system. Check vacuum lines. The TB shouldn't make any noise if the engine isn't running since there is no airflow. Try to record the noise

 

inside the cab?? maybe from your blower for your AC system.. have you isolated that down to see if it still happens with the fan and AC turned off?

 

still happening with ac turned off. in fact it happened again in the parking lot at work this morning but it was really weak. started dicking with it a little. it does the sound even when you dont actually start the engine. just whenever you turn the key on and off

 

Try recording the sound for us. Would make it easier to diagnose

 

I get a noise like you are describing but only with the ac/heat on sometimes.
My cutlass makes a little squeek squeek when I shut it off too. Idk what causes it. Wish I could help. Maybe its your surpentine belt.

 

this points to an electrical issue of some sort since w/o the engine on the coolant isnt moving, the freon isnt moving and the driveline/engine/accessories arent turning. need to figure out more accurately where it is coming from.