Back in the 60s Hybrid car radios did thump. I think that they had caps that discharged fast but the transistors picked up the power off surge before they lost power. I will do some research on that. I know my dad bought a new 1960s Ford Fairlane and It also POP'd or thumped either it was when it switch on or off. I don't remember which. Solid state was very new and designs were not fully understood.
_________________
I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!