The appliance may not be supported stably, or the load movement may reveal an existing floor or positioning issue. Stop using it in a way that risks tipping or sudden movement.
What the observation tells you
A folded piece of packaging placed underneath is not necessarily a safe long-term support. The correct adjustment method depends on the model and floor. Moving a heavy loaded cabinet can also stress its cable.
A useful next step
Describe when it rocks and whether the floor recently changed. Arrange competent positioning advice where needed rather than attempting a loaded lift or improvising wedges.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.