The Bombay stock Exchange's benchmark index Sensex bounced back in Wednesday's trade and closed with marginal gains amid volatility, on the back of buying interest in technology, telecom, pharma, cement, select metal and auto stocks.The markets witnessed consolidation throughout the session. The Sensex closed at 16,912.77, up 35.61 points. However, selling in banking, FMCG and oil & gas stocks capped the gains to large extent The National Stock Exchange's NIFTY gained 9 points, to settle at 5,042.05.