DIAGNOSIS That grinding noise is almost certainly the blade making contact with something it shouldn't. On this saw, the most likely culprit is the riving knife or blade guard assembly being out of alignment or bent.
FIX 1) Remove the battery. 2) Manually spin the blade by hand and watch/listen for where it contacts. 3) First, check the riving knife. Loosen its mounting bolt and see if it shifts out of the way. It should be perfectly aligned with the blade, not touching it. 4) If the noise persists with the riving knife removed, check the metal blade guard (if installed). It can get knocked in transport. 5) Finally, ensure the blade is installed correctly with the arrow on the blade pointing the right way and it's fully seated on the arbor.
IF THAT DIDN'T WORK A more serious, but less common, cause is debris in the motor housing or a failing arbor bearing. This requires disassembly you might not want to do. If alignment checks are clean, it's time to contact Milwaukee service.
HEADS UP Never ignore this noise and try to power through it. You'll ruin the blade, damage the guard or riving knife, and potentially cause a dangerous kickback situation. Always find and fix the contact before making a cut.