If they are clustered in a fuzz pile near the heat source and chirping loudly, then you need to up the temp a couple of degrees.
If they are spread out and doing their best to hide from the heat source and chirping loudly, it's a bit hot and you need to drop the temp.
If they are spread out all over the place, not panting, seem to be content in position, and still chirping loudly, then they have probably figured out that your shadow over the brooder means its dinner time and they are calling for the waiter to take their order.
They will also become more vocal as they grow and start to strain the space within the brooder. If you have checked and confirmed that everything else is okay, you may try pulling half out and moving them to a new spot to give them both some more room. This is more likely if they have hit that 2-3 week stage