The Nasdaq Stock Market announced Thursday that trading volume on ETFs reached a new record in September with an average daily trading volume of 785 million shares. That was part of a new record trading volume of 3.3 billion shares.

IndexUniverse says that ETFs now make up more than one-third of the U.S. market trading volume. They cite data from the National Stock Exchange , which says ETFs represented "a record 35% of all U.S. equity trading volume." That's up from 31% in August. Think about that: more than one-third of stock trades in America are for exchange traded funds.

Trim Tabs just came out with a report showing investors have been pulling money out of stock funds -- but throwing them into ETFs. Trim Tabs estimates investors took well over $40 billion out of all mutual funds in September, but meanwhile put about the same amount into ETFs. For the last 12 months, we've pulled $117 billion out of mutual funds and put $127 billion into ETFs.

For individual investors, the move makes sense. When the market is moving around like it has been, it's scary to be in a vehicle where you can only trade at the end of the day? But I can't imagine that all of that ETF volume isn't helping whip around the prices of the underlying shares.