Some commodity prices are soaring this year -- I'm looking at you, oil -- while other marquee commodities, namely gold, are sagging. Regarding the yellow metal and related exchange-traded funds (ETFs), these assets are slumping largely due to rising interest rates.In simple terms, higher yields refresh bonds' income proposition, making gold and bullion-backed ETFs less appealing because those assets don't pay dividends or interest. Gold's woes are pertinent to investors considering silver and ETFs such as t ...