I'm trying to figure out if this hose should be sealed completely or hissing if normal? Can't find anything on it any help is greatly appreciated

 

Can't imagine that it "should be" hissing. looks like it might be kinked , or at least a touch restricted, where it attaches to the coupling above center of the engine.
That hose isn't cracked is it near that kinked or restricted area? Maybe try putting a more flexible hose in there and see if it goes away. Or put some zip ties on the coupling areas
Is there any runability issues that are popping up as well?

 

Being apart of the heater assembly, it shouldn’t be hissing, this is late but I’d replace that part, it look corroded anyway