Snapshot spectra of four massive young stellar objects (mYSOs) in M17 reveal significant variability in line profiles that most likely originate in their circumstellar disk. In two of the mYSOs, the Balmer series, Ca-triplet and Paschen lines show significant change in the disk emission features. In another mYSO the peak-to-peak variation of the double peaked Paschen series and OI-lines changes over time. To our knowledge, this is the first time that spectroscopic variability has been detected in mYSOs. The observed variability (amplitude, velocity range, timescale) is key to better understand the physical origin of the emission lines, and thus the formation process.The aim of this project is (i) to measure the amplitude and velocity range of spectral variability of these mYSOs; (ii) to determine the characteristic timescale of this variability; and (iii) to identify the physical origin of this variability. Possible scenarios involve rotating disk structures, a varying accretion flow, and/or multiplicity. Characterising the incident rate and extent of variability as well as a timescale associated with this behaviour would be a first step toward systematic spectral variability studies of mYSOs.