Do not automatically buy an enclosure
Heat pumps are compact sources, often positioned close to walls and boundaries. Local shielding can work well, but airflow and service access must remain safe.
Absorption may matter
Hard surfaces can create reflections, making absorption useful in some layouts. In other layouts it adds cost without solving the dominant path.
Check vibration too
If structure-borne vibration dominates, a barrier alone will not solve the issue. Mounting and vibration isolation should be investigated first.