Update:

Knuckles has an upper respiratory infection. We noticed the sneezing on Saturday, but today was the earliest he could get in..

He is currently under the care of the adoption agency, on antibiotics, and scheduled for x-rays this Friday.

Turns out that he was with this when he arrived at our house, and the symptoms did not present until almost a week later....

We are waiting to hear from the agency if we get to have him back or not....

The thing that sucks that if it was our cat, we would have had him in last week, and would not have waited for the agency.....

Here's hoping the meds kick in soon......