METALS-Base metal prices fall ahead of Fed rate decision

(Adds analyst comment; updates prices) BEIJING, June 13 (Reuters) - Base metals prices fell on Wednesday, led by Shanghai aluminium, which touched a six-week low, as investors fretted over liquidity in China and awaited news from the U.S. Federal Reserve's policy meeting. The Fed is expected to raise interest rates at its meeting. Higher rates usually cause the dollar to strengthen, which would make dollar-denominated metals more expensive for holders of other currencies and could weigh