Beltron462

I have a used 17 Sierra 4x4 (first truck I've owned) that I bought last year. 30k miles. While the door was open today, I noticed that when i shift from reverse to drive, I get a "click" noise from near the back end (sounds like) when it hits drive. Does it almost every time. Does not do it when shift from drive to reverse or park, etc. I hear no other noises coming from this area any other time. Is this normal? It's almost as if it's the gear engaging, but I am by no means a mechanic lol. Thanks for any advice.

I have a 17 Sierra and it has plenty of rust underneath.

I was told by my dealer it was the fuel injector and normal on my 17.