Here’s the data:
https://fred.stlouisfed.org/series/FEDFUNDS
http://www.macrotrends.net/1333/historical-gold-prices-100-year-chart
I’m not sure your observation holds as a general rule.
One explanation for why it might hold in some cases is that investment is speculative. Investors may speculate that monetary tightening is done by the Fed because the Fed is expecting price inflation.
