Three decent slimline fans move the air. Yes, it really is free. No, they won't spam you.
Hard disks run hot.
There's air in there, and there's platters going round and round very quickly, and friction between the platters and the air makes heat. Drives can run surprisingly hot without having any problems, but the warmer the weather in your computer room and the faster your hard drive, the better an idea some sort of drive cooler becomes. They may last a bit longer with some airflow over them, but it really makes little difference. The 7200RPM drives most people use at present run warmer, but again generally survive OK without special cooling. But don't go nuts.