The legendary investor is making big moves with Berkshire Hathaway's stock portfolio.

The S&P 500 is down 2.6% over the three trading days this week as many of the big tech names that led the rally to a record in the summer falter amid overvaluation fears. Nvidia is down 24% from its intraday peak.

Key Takeaways Warren Buffett's Berkshire Hathaway sold more Bank of America stock to end August and start September, trimming its stake in nine straight trading sessions.The latest selling spree comes after the firm sold millions of shares in July after Bank of America stock hit a two-year high following an earnings beat.