My son is having changes in voice like a horse voice, but does not exhibit any other signs of cold like fever or runny nose. should i be concerned?

Yes,and how old?: age is very important in this kind of complain. hoarseness is a common complain, but it could a be a red flag for vocal cord problem including malignancy. so my advise if the hoarseness persisted see a specialist please

Maybe a little: could be allergies, but could be polyps or vocal cord lesions. I would worry more if he is having breathing issues especially with exertion. It may be worth seeing ENT.