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 US Bancorp (NYSE:USB) sank about 1% on Thursday after Goldman Sachs downgraded the banking giant from conviction list buy to neutral.

So what: Along with the two-notch downgrade, analyst Richard Ramsden reiterated his price target of $45, representing about 5% worth of upside to yesterday's close. So while momentum traders might be attracted to US Bancorp's price strength over the past several months, Ramsden's call could reflect a growing sense on Wall Street that its valuation is getting a bit steep. 

Now what: Goldman remains bullish on US Bancorp's growth prospects, but thinks that the price could be better. "[W]ith shares up 6% YTD relative to slightly negative EPS revisions, USB now trades at 12.2x 2015E EPS vs. sub-10.0x for money-center banks, 11.5x super-regionals and 12.1x for regional banks," noted Ramsden. "While we believe that this premium multiple is justified by USB's business mix, leading return on capital and minimal EPS volatility, we view the risk/reward skew at current valuation as relatively balanced." Given US Bancorp's seemingly stretched relative and absolute valuation, it's tough to disagree with Goldman's downgrade.