Pretty sure all you're hearing is the truck purging the lines of DEF. It does it a few seconds after you shut the truck off to clear the lines in case it freezes. It will also do it if you just have the aux power on as that will prime the lines. Its kind of like a suctioning noise, 2-3 times as you said.Hey everyone new to the forum. I've had my truck since it was new in July of 2019. Recently hit 48k miles and it is now "chirping" when you shut the truck off. It will also happen when you enter it after its been shut off and sitting. I have never noticed this before and not sure if anyone else has run into this. Seems like it will make the noise 2-3 times then stop. I asked the dealer to look into it when it went in for a recall this week and got the typical "we didn't hear anything."