DIAGNOSIS
A foreign object is trapped in the oscillation mechanism at the base. Coins or small toys are common culprits.
FIX
1. Turn the machine off and unplug it.
2. Tilt the loop backwards and look into the gap around the central pivot in the base.
3. Use a flashlight and a pair of long, thin tweezers to extract any visible debris.
4. Manually rotate the base a full 360 degrees to check for further obstruction.
IF THAT DIDN'T WORK
The plastic gear assembly inside the base may have cracked. This requires a service replacement of the base unit. Contact Dyson support directly; this is a known fault they often cover.
HEADS UP
Never try to disassemble the base yourself. The oscillation mechanism is under tension and contains a critical safety cut-off switch for tilt detection.