My 93 300D 2.5T has been making a clacking sound at around 1400-1500 RPM. It sounds like a valve clanking like sound. It only makes the sound when in gear. If I rev the motor in park - no sound. It is worse when cold, but doesn't go away when warm, just less pronounced. It is only audible at the specific RPM range. It sounds like it's the top back of the motor from the drivers seat but who knows if that is accurate. Anyone have any ideas what's going on. The motor has 125K on it. Power and shifting is normal and fine.