The floor must support the appliance and limit flexing during operation. Adjusting the feet corrects the seating; it does not prove that a platform or floor structure is rigid enough.
Level and rigidity answer different questions
A level lets you check the orientation of the surface or the appliance. Rigidity describes how much the support deforms under load. A floor can be level and still flex during spin cycles; it can also be rigid and still need the feet adjusted so all of them make contact.
The suspension reduces some of the movement, but it still transmits forces to the installation site. The noise that reaches another room can depend on that structural transmission as well as the sound radiated through the air.
Actual material and structure
Concrete, a platform, or an upper floor are not enough to declare suitability. Effective thickness and construction, condition, supports, and location matter. If the manual requires characteristics you cannot confirm, it needs evaluation by the installer or a structural professional, not a test involving violent spin cycles.
Bases, pads, and wheels
A soft carpet can change stability and make even support harder. A wheeled base must be approved and locked in the intended way. Pads do not fix insufficient suspension or flooring.
The pedestal adds height and forces on fasteners. Before installing accessories, verify the compatibility of the full setup and access for servicing. Then apply the corresponding leveling.
If a machine that used to be stable starts moving, do not assume the floor is the problem: the change may come from load, fasteners, or components. The rated noise reading also does not diagnose that behavior.
First confirm the support, then the seating; adding a layer under the machine replaces neither check.