I recently bought a 1999 35th anniversary Mustang V6 (5 speed). Within the few weeks I've had it it has ran well and sounds very clean. The only sound that worries me was and is a odd "knock" sound as I let off the clutch in 1st gear. I thought nothing of it since it's my first standard transmission vehicle, until tonight. I was driving through downtown and came across a rough railroad crossing. I had slowed down as soon as I could, but i still hit it going 25-35 mph which made for a rough crossing. After that the knocking sound followed up into second gear and now I am extremely paranoid. I would like to hear what you guys think it could be. Thanks for your time.