NEW YORK (CNN/Money) - Shares of Sirius Satellite Radio rallied again Tuesday afternoon and topped the Nasdaq most active list amid speculation that companies may be looking to take a stake in the subscription radio firm.

After falling in pre-market trading Tuesday, Sirius (SIRI: up $0.11 to $3.61, Research, Estimates) shares changed course at midday and climbed nearly 4 percent on heavy volume -- more than twice the volume than the second-most heavily traded stock on Nasdaq.

"It's probable that companies are looking, because they don't have a strategic investor," said one equity analyst who asked not to be named out of concern of fueling the rumors.

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Strategic investors, often major corporations, are actively involved in a company's operation.

Competitor "XM Satellite has General Motors, so it's pretty easy to make the leap that a looker is going to make the jump and take a stake in Sirius," he said.

Clear Channel Communications (CCU: Research, Estimates) surfaced as having a possible interest in Sirius, according to market participants, after Clear Channel said it will sell 15.8 million Univision shares back to Univision. At Tuesday's prices, the transaction would net Clear Channel about $605 million, a sum that could be put to use on other investments.

Representatives from Clear Channel or Sirius didn't immediately respond to calls seeking comment.

Kit Spring, analyst with Stifel Nicolaus & Company, doesn't believe that Clear Channel is interested in Sirius, although he added other companies may be taking a look.

"Rarely does Clear Channel make an acquisition that isn't accretive to earnings, and Sirius wouldn't be accretive, and Clear Channel also has a seat on XM Satellite's board, which it would probably have to give up if it wanted a stake in Sirius," Spring said.

However, Spring says talk of companies looking at Sirius is out there, adding that another interested party may be satellite TV firm EchoStar Communications (DISH: Research, Estimates).

"EchoStar rumors have been out there in the past, and that would make more sense," Spring noted.