Looks like investors are listening to a warning from Netflix (NFLX) CEO Reed Hasting.

Shares of Netflix are down over 4% from Monday's close to under $340 despite a seemingly brilliant third quarter earnings report that sent the stock up 10% in afterhours trading.

Why the fall? Some analysts are trimming their ratings, with Tuna Amobi of S&P Capital IQ downgrading the stock to "sell" from "hold." But also weighing on the stock are Hastings' comments made midway through the company's video chat with analysts.

Hastings usually prefers to brush aside questions about his company’s sometimes-volatile stock price. But with shares of Netflix up 18% on Monday including after-hours trading – and having nearly quadrupled in total this year – Hastings decided to issue a warning.

“Every time I read a story about Netflix is the highest appreciating stock in the S&P 500 it worries me because that was the exact headline that we used to see in 2003,” Hastings said.

The company’s shares had been riding a wave of euphoria. Subscriber growth has accelerated amid a string of hit original shows like “Orange is the New Black” and "House of Cards," which won the company its first Emmy awards for content. Netflix even surpassed Time Warner’s (TWX) Home Box Office with 31.1 million total U.S. subscribers at the end of the third quarter.

Netflix said it earned 52 cents a share, beating analysts' estimates of 48 cents and four times the 13 cents it earned in the third quarter of 2012. Revenue rose 22% to $1.1 billion. The company added 1.3 million U.S. subscribers during the quarter.

This year, Netflix shares had shot up from under $100 to $355 as of the close on Monday. After hours, the shares almost touched $400 before finishing at $392.50.

“We have a sense of momentum investors driving up the stock price more than we might normally,” Hastings said on the company’s videocast. “There’s not a lot we can do about it. But I wanted to honestly reflect upon that.”

Back in 2003, Netflix raced from $11 to $55, split 2-1 in January 2004, then plummeted all the way back down to $11 in November.

Some analysts were also wary of the stock, which trades at a price-to-earnings ratio of close to 300.

Hastings also said the company is preparing to offer customers even higher definition programming than current HD TV standards.

“We want to be one of the big suppliers of 4K content next year,” Hastings said, referring to the industry’s next generation standard with even more detail than HD.

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