A pallet with corrugated boxes is also a spring-mass-system. But the system has many springs and masses.
You have the same spring constant between all boxes but different mass over each layer. The typical spring constant and masses in pallets create own frequencies between 2 – 20 Hz. Please look in A2. Measurement of Vibration and you will realise it is in the same area transport means have a lot of inputs to a pallet.