A fairly blunt approach I'm afraid.
Suggest laying the brute as bare as you can (cover off etc.)
Then check your temperature after a good spell of running. If it is appreciably cooler you can look to better case cooling.
BUT I undestand the Athlon range do run hotter than many, and am afraid I know no figures to say what is the safe limit.
I assume the CPU fan appears to be up to speed and doesn't produce chattering, stumbling noises?