Unknown Sickness

The other day, I picked up Meow. Just a normal way to pick him up; under his front arms, sort of on the chest. He made a squeak the the second I began to lift him. I was scared that I hurt him, and ran to tell someone. We though maybe something was bugging him, such as he ate something strange. He does that all the time; eats things like the window screen or wrapping ribbon. We didn't think it was anything serious, so we kept an eye on him, and didn't pick him up. A couple of days later, I went to pick him up again, after we had picked him up before, and I was demonstrating to a friend how I had picked him up previously. He squeaked again. I am thinking that it may be something he ate, or maybe he just isn't feeling well, with a cold or another sickness. But he isn't acting mopey or sad. He's just acting as normal as he always does. I am unsure what he is bothered by.