Why Sirius XM Stock Just Jumped 8%

Sirius stock looked cheap a month ago, and it still does today.I argued last month that given a price-to-free-cash-flow ratio of 10, "dividend payments at about 4.3% annually," and plans "to buy back $1.2 billion in stock ... the case for buying Sirius XM Holdings (SIRI 8.70%) stock is only getting stronger."Turns out, someone was listening.Shares of Sirius stock gained 8.1% through 10:45 a.m. ET Monday after Warren Buffett investment vehicle Berkshire Hathaway (BRK.A 0.15%) (BRK.B 0.26%) revealed in an SEC ...