This tune sounds familiar.

Apple (Nasdaq: AAPL) may command just 28% of this country's prerecorded music sales market, but that's apparently enough to trigger an investigation.

The Justice Department is reportedly making preliminary inquiries into Apple's pricing strategies and business practices.

Is Apple too powerful? Research giant NPD pegs Apple's share of music sales at 28%, but that figure includes CD sales. If we boil it down to digital music, Apple's iTunes commands a cool 70% of the market.

This is problematic for regulators since it's the one form of music distribution that's actually growing. As CDs fade, Apple's share will get even larger. (Nasdaq: AMZN) has caught up with Wal-Mart (NYSE: WMT) for a second-place tie in overall music sales. Both companies command 12% slices of the pie, but that only means that Apple is selling more music than the leading online and offline retailer combined.

Suddenly, 28% seems like a pretty thick slice.

Briefly in the news
And now let's take a quick look at some of the other stories that shaped our week.

  • Market turbulence isn't getting in the way of mergers and acquisitions. IBM (NYSE: IBM) is buying AT&T's (NYSE: T) Sterling Commerce. The $1.4 billion deal gives IBM some new skin in the electronic data interchange market.
  • Sirius XM Radio (Nasdaq: SIRI) is a volatile beast, even when there's no material news. Shares of the satellite radio operator plunged 11% on Wednesday, but more than made that up with a nearly 14% spike on Thursday.
  • Wal-Mart began selling Apple's iPhone -- the 16 gigabyte 3GS model -- for just $97 on Tuesday. This is less than half of its original price, and just one more reason to expect the next generation of iPhones to hit the market over the next few weeks.

Until next week, I remain,

Rick Munarriz

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Longtime Fool contributor Rick Munarriz recommends windshield wiper fluid when trying to look back. He does not own shares in any of the stocks in this story. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.