My main desktop computer is in an Antec P180 case. Most / all? of its outer panels are made of aluminum - plastic - aluminum material. They make a particular dull sound when knocked.
I’m talking about drive enclosures made by storage companies. The EMC, NetApp, IBM, HP type of places. Consumer grade cases all use the cheapest sheet metal they can find.
The P180 has these walls for their sound dampening properties. The material is for sure not cheaper than mild steel, which is what cheap cases are made of.
