All the computer fans I've ever examined have "stick-on" adhesive labels on them. I just ease 'em up with a sharp blade and insert some grease into the bearings and cover the hole up again - till the next time I'm delving inside the case to track down noises. Anyway, it's a good idea to remove the side panels & check that the CPU *&* the videoboard fan (if fitted) is whizzing around.... And NO - you don't stick a finger in to check - the computer doesn't require any blood transfusions!.
Anyway, if the computer is still under warranty - and under "Home Service" as opposed to "You gotta haul it in to our service dept" - then call out the Dell service people. Cleaning up a computer fan is little difference to cleaning up the blades on a "keep me cool" floor-standing fan.
If you can inject graphite grease - not too much - into the bearing, it'll last for a looooooong time.
I can't find a source of graphite grease!