Loud knock after changing lower intake gasket 4.3 07 sierra

[RedNeckTexan]

Hey y'all first time posting. Y'all are an absolute array of knowledge I thank y'all for all y'alls comments. 

So I purchased this truck about a year ago and it started having a lower intake manifold leak I ignored it for a while just made sure it had plenty of coolant. I finally changed it the other day and I went to start it and I was a loud knock. After cranking it a couple times did not seem to not be there. Also after trying to start it about five times it would fire but not run. I have not tried to start it again because of the knock. There was a lot of calcium buildup that look like from water instead of coolant being used. I would like to hear your opinion on what you think the knock is I was so careful to not drop anything I do not think it is that. Thank you for all your comments.

Zachary K.

[BarryKH]

You didn't let any water get in the intake ports on the heads when removing it did you? If so may have water run down into cylinder and trying to hydro-lock. Take the plugs out and try turning the engine over and see if the knock is still there. Water will not compress.