Sirius XM (SIRI) shares rose 2% Tuesday after a Citigroup (C) analyst upgraded Liberty Media (LMCA) and speculated that Liberty could soon have a controlling stake in the satellite radio giant.

Liberty has been so loud about its intentions to purchase Sirius that it could blow out a subwoofer with the back chatter. Liberty has snapped up even more of the company since buying 12.5 million preferred shares, roughly a 40% stake, to save it from bankruptcy back in 2009.

Its current stake stands at more than 49%, and a recent letter to the Federal Communications Commission indicates Liberty may have a few thoughts about shuffling Sirius' current board. Tuesday, the FCC announced it will allow the public to comment on Liberty's plans to swallow up Sirius.

This already has nervous observers suggesting Sirius investors sell while they can, noting Liberty's 49.5% stake in Sirius is supplemented by a 32% grip on common shares. Gabelli & Co. thinks that's overplaying Sirius' value, and it downgraded Sirius XM's rating to "sell" last week.

But Liberty CEO Greg Maffei seems not to be in a rush to make a big move and may want to help Sirius grow a bit more before taking the reins. Meanwhile, Spencer Osbourne at Seeking Alpha cautions that there's still cash to be made off Sirius shares from "profit potential, leverage, and share buybacks." As for that "sell" rating, Sirius shares just hit a 52-week high on Tuesday.

There's also the small matter of Sirius' growing subscriber numbers, particularly within the auto sector. Despite increasing subscriber fees back in January, Sirius managed to increase revenue, subscribers and net additions. At the beginning of 2012, the company predicted it would add a scant 1.3 million subscribers this year compared to the 1.7 million it added last year. As subscribers warmed to the new fees, and as new subscriptions from auto partnerships increased with car sales, Sirius hiked its new subscriber estimate to 1.6 million. If a forecast of 14 million new car sales for 2012 holds, that may make Sirius' latest estimate seem conservative.

Liberty Media still has its eyes on Sirius, but Tuesday's upgrade is just a small step toward a bigger satellite radio acquisition. If this takeover process was a song playing on a Sirus XM station, this latest upgrade would be an early note in a long, noodling guitar solo. Take a seat and enjoy the show.

Sirius shares rose 2.1% Tuesday to close at $2.62, and Liberty Media shares rose less than 1% to close at $105.47.