Mild vibration is normal. Heavy shaking that rattles the wall or makes the unit "dance" = a problem. Usually mounting or compressor age — sometimes a fan that lost balance.
See if any of these signs match your device — each one increases the likelihood of this fault.
These are the causes we encounter while repairing AC vibrating heavily — ranked from most to least common.
Outdoor bracket bolts loosened
Rubber compressor mounts deteriorated
Outdoor fan lost a blade or its balance
Compressor internal imbalance (older models)
Indoor unit installed flush to wall without isolator
Any of the following = a danger signal — call now and don't try to fix it yourself.
On-site diagnosis, clear pricing before any work, and a documented 6-month warranty.