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I am sorry to hear that your boy is having these problems.
A couple of things that could be going on are:
-the excessive barking as you suggest
-a respiratory infection such as kennel cough. While the vaccine helps in most cases, it doesn't completely eliminate the possibility of an infection.
If he starts coughing at home in the next day or so, you will have some idea about kennel cough.
Otherwise, if he is eating and drinking well, I would expect his "voice" to return to normal in 2-3 days. If it does not, or if he is not eating and drinking well, he should be evaluated by your veterinarian.
I hope this helps!
As always, if you have further questions or concerns, please don't hesitate to ask them using the "reply" function.