It's quite common.
Is there any chance the viv is too big?
If so you can add more decor/plants - make him feel more secure. Other than that try sliding the doors open and letting him bring his head out of his own accord, might be a bit easier.
Also, don't show fear. Don't back down and leave him because he is being grumpy. That will make him think that the more he hisses the quicker you will go away!
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