Sounds Popping noise when "talking"

[rolandinthehay]

Alfie makes this popping noise when he is "speaking". I only ever notice it when I pick him up and he is about to start making normal guinea pig sounds. At first I thought it was a sign of pneumonia (he had a URI), but he was on Baytril for 2 weeks and the rest of his symptoms cleared up. He is going to the vet on Wed morning for a check-up, but until then I wondered if anyone else had experience with this sound?

I have tried to get a recording of it, but since it only really happens when he is talking, the guinea pig talk overpowers it on the recording. So frustrating.