The presented study examines the effect of voltage subharmonics, which relates to components of the frequency less than the fundamental voltage harmonic, and the currents and vibration of the line start permanent magnet synchronous motor. The obtained experimental results corresponded to a production motor with a rated power of 3 kW and a rated speed of 1500 rpm. The main purpose of our study was to highlight that the subharmonic value had a non-linear effect on the vibration level of the considered motor. It was found that for subharmonic values up to approx. 0.5% of the vibration level could be considered acceptable for long-term operation, whereas vibration caused by voltage subharmonics of values greater than approx. 0.8% might promote machine damage.