If its a fan, it may just be loose (maybe whoever repaired it didn't secure it properly). As previously noted, Dell fans are proprietary.  Aftermarket fans will work but you will get a fan failure notice at power on and will have to press a Function key to continue.  
I have a weird issue with Inspiron 7577 and that issue is when I tilt the laptop I hear a loud noise comes from the left fan, sound like a mouse clicks with a loud noise and it doesn't stop unless I restart the laptop, once I restart it the fans are so quiet and comes back to normal, I've already replaced the thermal paste on both CPU & GPU and nothing's wrong with the temperature, that noise only happen when I move the laptop and like I said once I restart it that weird sound is gone, and by the way there's no original fans for this laptop available where I live, can I continue using the laptop without concerns? Or I should replace them with the unoriginal ones? My warranty is over as well, all I want to know is can this issue affect anything inside or that is something normal and I shouldn't worry about it?  Thanks in advance
Inspiron 7577 weird issue