Momentum investors are stock players who get behind companies that have the wind in their sails. Contrarian investors typically pick up the cigar butts the market has tossed aside. So what do you call investors who turn against winners? Sourpusses? Shorts?

Over on Motley Fool CAPS, we sometimes call them the savviest investors around. Not only does the 73,000-strong investor intelligence community rate thousands of stocks every day, but the players themselves get rated, too. The best of the lot -- what CAPS calls All-Stars -- consistently outperform their peers over time and are assigned ratings of 80 or greater.

When an All-Star player sours on a top-rated stock, perhaps we should take notice. Perhaps the player's found a chink in that highflier's armor, or a question mark in its financial footnotes. Or maybe it's just a hunch. That's why these tables aren't lists of stocks to buy or sell -- just starting points for further research.

Here's a list of stocks that some All-Stars have given a thumbs-down to:

Company

CAPS Rating

1-Year Return

CAPS All-Star

Player Rating

Aluminum Corp. of China
(NYSE:ACH)

****

264.9%

phi16

98.99

Garmin (NASDAQ:GRMN)

****

107.9%

redearth329

94.17

China Petroleum & Chemical
(NYSE:SNP)

*****

105.7%

traviskang

92.62

Suncor Energy (NYSE:SU)

*****

39.4%

traviskang

92.62

SanDisk (NASDAQ:SNDK)

****

(10.9%)

Squant7

95.03

With more than 8,200 ratings on these stocks, 96% of them are bullish, with some 97% of All-Stars also thinking they'll outperform the market. So what might have turned some of CAPS' top players against these otherwise widely admired companies?

Finding your way to Garmin
It wasn't too long ago that GPS maker Garmin was a five-star CAPS stock, leading a group of mostly privately held companies. But the market for personal navigation systems has tightened up, and the companies that actually make the maps for the GPS systems are getting gobbled up. Garmin has joined in the bidding for them with its recent bid for Tele Atlas.

Is Garmin crazy like a fox in trying to force rival TomTom to pay more for the mapping source by matching its bid? That could be, since Garmin gets its maps from Navteq (NYSE:NVT), which itself recently agreed to be acquired by Nokia (NYSE:NOK).

Yet the uncertainty remains, and the Motley Fool Stock Advisor recommendation could end up being the one to overpay. That may be what's causing some otherwise astute investors to map their strategies against the GPS maker.

That's what has top-rated CAPS All-Star ikkyu2 betting against Garmin. He thinks Nokia has Garmin in its crosshairs:

There's a real fear that by buying Navteq, Nokia is setting up to produce its own line of devices. They could easily simply stop selling maps to Garmin.

Garmin's $3.3 billion bid for Tele Atlas proves that the Garmin board believes this scenario to be true. They have to overpay for [Tele Atlas] because if they don't they'll go right out of business. They know it.

They're going to go out of business anyway. The only way they don't is if FTC or some other regulatory entity blocks the acquisition of NVT, and unlike Unocal, I fear that NVT is going to fly right under the regulatory radar.

Make lemonade
We know both sides here, but Motley Fool CAPS is more than what some pros think, even if they're All-Stars. It's where we invite you to share your thoughts and insights and add your voice to the debate. Go ahead and have your say. We're eagerly waiting!

Garmin is a Stock Advisor selection. You'd end up loathing yourself if you didn't take advantage of the 30-day free trial subscription available at no risk.

Fool contributor Rich Duprey does not have a financial position in any of the stocks mentioned in this article. You can see his holdings here. The Motley Fool has a disclosure policy.