Knock Knock

[MWood]

Hello fellow GMCers ;-) I have a 99 Sierra 1500 w/ approx 65,000 miles. Recently, over the last few months, I've noticed a thunk coming from within my gas tank... maybe. Initially it happened a few minutes after the truck was turned off, but now I notice that it also happens a few moments after I start it. This is not a continuous thunking, just one simple thunk after start up and again one simple thunk after I turn her off. Is there a little someone who found themselves stuck in there or something? I replaced my fuel pump about five years ago, and I did not realize that regularly changing the filter is necessary. I am also guilty of running my tank down to less than a 1/4 - yikes!

[txab]

Might be an emission part. Evap valve and all that.

 

Seems like recall hearing that the emission system can make a little noise