Why is my MacBook getting hotter than usual since some time? Since some time my MacBook is constantly hotter than it used to be, even when not having much CPU load. What could the cause be?

Resetting the System Management Controller (SMC) didn't completely work, I think it has decreased since I reset it but not completely.
Sometimes is is good to reset the SMC.

SMC controls the devices on your computer including the fans.

Intel-based Macs: Resetting the System Management Controller (SMC)