Why does my Android phone charger cause my (powered-off) stereo receiver to make a high-pitched chirping sound when plugged into the same powerstrip?
(Do not be cruel. I have tinnitus. It is like your worst nightmare come true.)

This could be magnetostriction, or clashing PWM supplies. The chirps could be core noise or frequency ratios mixing at a core.

Suggest power strip with CM chokes as EMI filters. Pay the cost. Fix the problem.