Engine/Transmission (1994 - 1998) bubble/air sound from heater core durring startup

[HotRodCummins12v]

i am having this problem with my truck mostley when its pretty cool, in the morning, only started doing it recently. also my buddy heard it on his 2001 HO. anybody else notice this sound? is it normal?

 

[vssman]

I get that same gurgle once in a while too. It's been there since day 1. As long as I get decent heat in the winter and it doesn't over heat in the summer, I'm not worrying about it.