Aloha! You're speaking with Dr. Michael Salkin I don't know of any mechanism for a furball to cause a change in vocalization at this late date. You're on the right track, however, because such a change does involve the vocal chords when they're infected by either the feline herpesvirus (FHV-1) or the bacteria Bordetella bronchiseptica. Persistent gastroesophageal reflux (GERD, acid reflux/heartburn) is a consideration as well. Most of these cats remain normal otherwise and will remiss unaided within 1-3 weeks. As long as Ollie continues to be "perfectly happy otherwise" there's no reason to have his vet attend to him. Please respond with further questions or concerns if you wish.
Thank you for reply regarding our silent Ollie. As this problem has been ongoing for 3 weeks already hopefully it will clear up unaided soon, as you suggest. Should I try a little olive oil in his drink to soothe the situation or perhaps a lick of manuka honey?