Thank you for your message. This system model has 2 fans which share the heatsink, one for the CPU & the other for the GPU.
Not necessary that the fan spins at the same time on both sides.
Have you observed any heating issue lately? Please make sure that the air vents are clear off any dust.
For my reference, please click on the message tab next to your avatar– click “New Message” & search for my Dell username (Sreejith R) & send a private message with the service tag, registered name & email address.