It took almost 20 years for any conclusive proof to arise that JPM had a colossal short silver position.... and that evidence came from them saying something like "Yes, we have a sizable short silver position, but it's a hedge rather than anything meaningful."
It also wasn't very hard to find an NYT article on the metal in question. According to the NYT, Goldman isn't hoarding aluminum. They're storing it for other institutions.
The price increases aren't a result of an aluminum hoard as much as they're a result of Goldman being a really shitty warehouse operator that managed to increase the time it took to get the metal from one warehouse to a customer from 6 weeks to 16 months.