Lael Brainard is a Governor of the Federal Reserve System; she spoke earlier today (late US time):

In part, Brainard warned:

  • High asset prices and growing economic pressure from U.S. fiscal stimulus mean financial markets may be particularly vulnerable to an unexpected shock,

That is via Reuters run-down: Fed watching for financial shocks as risks build: Brainard

For more,

Bloomberg:

and the (gated) Wall Street Journal :