My 2 year old Siamese cat has recently changed the tone of his meow, what can cause this?

I'm a little worried, just yesterday morning he was meowing fine with his usual high pitched meow and late that night it became coarse, like he was loosing his voice. He is usually very vocal, but I don't think that can cause a cat to loose their voice... can it? He hasn't been displaying any signs of an upper respiratory infection and his behavior has not change. Has anybody experienced this? If so, what was the cause? I will take him to the vet in the next couple of days... I'm just anxious and worried now.