The battle for eardrums is coming from all directions at Pandora Media (NYSE: P).

The latest attack comes from Clear Channel (OTC BB: CCMO.PK), which is relaunching its iHeartRadio app. The revamped application from the terrestrial-radio juggernaut won't officially roll out until the end of next week, but it became available in beta form last Thursday. Anyone who simply clicks "like" to become a fan on its Facebook page is given immediate access to the streaming service.  

It's apparently pretty popular, since more nearly 1.2 million people have "liked" the iHeartRadio page. I gave it a test run over the weekend and walked away pretty impressed. The original application provided streaming access to roughly 800 Clear Channel radio stations. If you don't like the station you're hearing, clicking the "scan" button works the same way as your car stereo. However, instead of being whisked away to the next local station on the radio dial, you're sent into one of Clear Channel's hundreds of channels throughout the country.

Clear Channel's iHeartRadio has been popular in its original incarnation. It's been downloaded more than 34 million times as a mobile app. Clear Channel is serving up about 50 million listening hours a month.

Pandora may not feel threatened right away. It delivered 1.8 billion hours of listening in its latest quarter alone. However, the new iHeartRadio raises the stakes by offering users the ability to create their own stations by choosing from 11 million songs by 400,000 artists -- far more than Pandora's thin catalog.

Pandora can counter that this is a matter of quality over quantity. Pandora's "music genome project" identifies musical traits that a registered user likes based on his or her streaming preferences, offering up great suggestions in what is truly a music-discovery experience.

However, music fans know a good deal when they stream it. Pandora users need to become paying subscribers if they want to zap intermittent ads. Clear Channel is offering up iHeartRadio's custom stations for free without any commercials through the end of the year.

Spotify marks the spot as Facebook faces the music
It's not just Clear Channel that's gunning for Pandora's booming audience. European sensation Spotify launched in the United States this summer. If iHeartRadio's library is massive, wrap your earbuds around Spotify's catalog of more than 15 million songs that can be fully streamed on demand.

The only downside to Spotify is that it's not available as a free mobile app, even for those willing to put up with commercials. There is a free ad-supported version that runs only online, but mobile streaming bears a price of $10 a month.

If we're talking premium, Sirius XM Radio (Nasdaq: SIRI) is heading for a major upgrade to its receiver platform later this year. Sirius XM 2.0 will hit retailers later this year, with automaker-provided installations starting up as early as next year. Sirius XM also offers existing subscribers streaming access for $3 a month.

Then we get to Facebook. The social-networking site with more than 750 million active users is widely expected to announce a music-streaming initiative when it hosts its f8 conference next week.

Oh, and let's not forget the big boys. Apple (Nasdaq: AAPL) and Amazon.com (Nasdaq: AMZN) have launched intensified cloud-based music offerings in recent months. Few observers see Apple's premium music platform and Amazon's digital-music locker as threats to Pandora, but that's where they're all eventually heading.

Are the gravy days of Pandora -- brief as they may have been -- over?

Pandora battles back
Thankfully, there's plenty of demand for streaming to go around.  Pandora's latest quarter was a strong one, with revenue soaring 117%. The streaming leader even managed to post a profit on an adjusted basis.

Pessimism is already baked into the shares, which now trade well below June's IPO price. That obviously doesn't mean the stock can't head lower, especially if the growing number of competitors circling the streaming wagon attack hard.

In the end, all of this attention validates Pandora's niche, but it's going to put pressure on its pricing and perhaps even what it can negotiate out of lead-seeking advertisers.

Summed up in one word: cacophony.

If you want to see how Pandora stands up to the streaming upstarts, add Pandora to My Watchlist.