Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: This has to be getting tiresome. After big declines in June, July, and August, shares of Clearwire (Nasdaq: CLWR) closed down another 11%. This time, worries over the cost to bring Apple's (Nasdaq: AAPL) iPhone to its parent carrier, Sprint Nextel (NYSE: S), appears to have caused the selloff.

So what: Like a climber stuck in an avalanche, investors sold on fears that fresh commitments to Apple could leave Sprint unable to provide additional financing to cash-strapped Clearwire.

Now what: It's a fair concern. The WiMAX specialist's debt is virtually equal to equity and 50% of total capital as of this writing, a structural weakness that begs for help that Sprint isn't in a position to provide. Do you agree? Would you buy shares of Clearwire at current prices? Please weigh in using the comments box below.

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Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team. He owned shares of Apple at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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