What may be the cause of this? It happens every time when I build the app on either simulator or device.
Should i clean sth or reset my harddrive?
using High Sierra and Xcode 9.2
It is enough to open Xcode and it hums the same way.
The 2015 MacBook Pro uses a Solid State drive, so there's nothing on it that going to "hum."
In fact, the only mechanical component in the MacBook Pro (besides the keys and LCD hinge, of course) is the fan. The fan may be spinning up due to the increased load put on the CPU. Additionally, it may be clogged with dust or the bearing is simply defective.
Try giving it a cleaning and see if the problem goes away. There's no need to "reset" your drive as this would have no effect.