I've spent the last hour or so setting up the pitch and throttle curves on my bird and noticed that it's getting pretty toasty during use.
Make sure you have your antenna pulled out about 1/4 of the way when your just setting at the bench setting up your heli, from my understanding, if you don't have the antenna pulled out some the radio will get hot.
If that doesn't fix the problem, I would give Hitec a call and ask them about it (you don't want to burn your new radio up).