DIAGNOSIS The main feed gear train has a misaligned gear or a foreign object jammed in it. The plastic gears can skip teeth under high load.
FIX Turn unit off, remove battery and tape cartridge. Look into the tape path with a flashlight. Use tweezers to remove any bits of cut tape or debris. Manually turn the large white feed gear by hand to feel for resistance. If it turns smoothly, the issue was debris.
IF THAT DIDN'T WORK The stepper motor shaft may be bent. This requires disassembly. The motor is a 28BYJ-48 type. If the shaft is visibly bent, the motor must be replaced. You cannot straighten it.
HEADS UP This noise often happens after a tape jam. Never force the tape through by hand while the machine is on. You will strip the plastic gears.