US stock futures waver as Nvidia's blockbuster results draw muted response

US stock futures are experiencing volatility despite Nvidia's stellar earnings report. This muted market response suggests that while Nvidia's results were strong, investors may have already priced in much of this positive news, or are exercising caution due to broader economic concerns. The wavering futures could signal a 'buy the rumor, sell the news' phenomenon for some tech stocks, and highlight a potentially fragile market sentiment moving forward.