Some hamsters are more vocal than others but it’s strange that this a change in behaviour. As said already by Ria though it may be the heat, try putting some ceramics around the cage or an ice pack against where he sleeps to help him cool down.
If it’s a very sudden change he probably is trying to tell you something, I also wonder if this has been a gradual change, maybe he’s just trying a bit older now as they tend to slow down a bit then. But from what you said it sounds sudden so I would try and hunt down the source of why he’s chirping
