Sirius XM Holdings Inc. shares SIRI were rocketing 17% in premarket trading Wednesday after Warren Buffett’s Berkshire Hathaway revealed a new stake in the satellite-radio operator. Berkshire bought up 9.7 million shares of Sirius during the September quarter, worth $43.8 million as of the end of the period, according to the company’s latest 13-F disclosing its holdings. Shares of Sirius have declined 16% so far this year, as the S&P 500 SPX has added 17%.

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