2001 Ford Focus Loud Engine

Engine problem
2001 Ford Focus V4 Two Wheel Drive Automatic 74,000 miles

When I warm up the car, the engine is extremely loud upon starting and continues until driven for a period of time. There is a small vibration inside the car. (The noise is less if I'm sitting at a stop light and put it in neutral)

The vehicle was purchased new in 2001 and the maintenance has been kept up very well - oil change, transmission, etc. We've always used the same type of gas in the vehicle.

Can you give us an idea of what may be the problem?

Thank you for your help!