While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Noble Corp. (NYSE:NE) bucked today's downtrend after Standpoint Research upgraded the offshore drilling contractor from hold to buy.

So what: Along with the upgrade, analyst Ronnie Moas planted a price target of $38 on the stock, representing about 22% worth of upside to Friday's close. While momentum traders might be turned off by the stock's weakness in recent months, Moas thinks that Noble represents a particularly timely buying opportunity given its historical trading pattern.

Now what: According to Standpoint, Noble's risk/reward trade-off is pretty attractive at this point. "The drillers have been hit hard recently and that has created some opportunities," Moas noted. "NE is a name I exited two years ago @ $41 and it has underperformed the S&P by > 5000 bps (and underperformed the XLE by 4000 bps) since then. This is a name you could have gone into at $30 and exited at $40 six times in the last ten years." More importantly, with the stock boasting a 4.5%-plus dividend yield and trading at a forward P/E of 7, Noble looks fundamentally inexpensive as well.