Why can I feel vibration when I touch my network switch or streamer?

I have a Silent Angel Bonn N8 switch powered by a Forester F1 linear power supply, which is attached to an Innuos Zen Mini Mk3 with a SSD, also powered by a linear power supply.  The N8 and Mini sit on top of their power supplies.

When I lightly touch the top of either the N8 or Mini, I can feel a slight vibration.  I am surprised by this because neither device has any moving parts that I know of.

Why does this vibration occur?  Is it inherent vibration of the electrical parts within the devices (e.g., resistors, capacitors)?

Would I be well-advised to avoid stacking the N8 and Mini on their power supplies?

Should I simply decrease my coffee intake?