The goal of this study is to examine the effect of the number of slots on the noise from BLDC motors. To this end, the number of poles was fixed to 4 and the number of the slots was set to 6 or 24 before noise was measured. Motors having different numbers of slots showed clear differences in noise. Cogging torque, torque ripple and normal local force were interpreted, analyzed and compared to determine the reason for the differences. To determine the cause of the noise, cogging torque, torque ripple and normal local force were calculated, which are representative noise sources of BLDC motors, and FFT was performed to analyze their frequency components(harmonics). The results show that torque ripple and normal local force were the dominant factors in the noise difference between the 6-slot and 24-pole motors. As the number of the slots increased, the number of harmonics decreased and their amplitude of harmonic were reduced, which was attributed as the reason for the noise differences.