Take the centre cap off the wheel that makes noise, remove the 13mm (1/2”) headed bolt and remove the wheel. Guaranteed the plastic drive gear that is screwed to the wheel has stripped teeth. There is a metal gear available now that supersedes the plastic gear. Call customer service and inform them. If you use the self propel in right turns, it strips the gear that is screwed to the inside of the drive wheels.
Read page 31 (15-0910_EGO_LM2100SP_LM2100_56V_Lithium-ion_cordless_mower_manual_NA_V1_online) about removing the rear wheel...examine the gear on the axle to make sure it is still cleanly meshing with the drive gear