I can hear mine working, like when I get off the hi-way and come to a stop. Then when I take off I can hear the sound of my fan, it's louder. Then as it cools off the fan get's quiet again.

I have had 2 car's over the years that overheated at slow speeds or idle, both times new fan clutches fixed my problem and I could hear the fan again when it was hot. I have a 7 blade stock fans.