Well the flashing light is just a tiny low current neon tube that can't hurt anything. The main thing to worry about with power strips is that they securely hold the connectors in place and not overloading them with more than their rated power, and the power of the circuit they are attached to in your home.

Switching power supplies for cheap consumer stuff are usually operating in the 20-30 kilohertz range. This is just outside of the audible range. What you are hearing is usually the windings or powder ferrite core of the miniature transformer physically vibrating. The audible sound is likely some lower order harmonic resonant peak that is in the audible range.

At the manufacturing level, the frequency of switching can be tuned to avoid unwanted noise, and the magnetics can be potted in a resin or other techniques used to dampen the vibrations. If you build your own power supplies like I have, they tend to make a lot more noise at the first prototype stage.