I have had my S40, 18,000 miles, regular engine with standard 6 speed transmission for several weeks now. I am not sure of what is normal sounds for the car. It seems to me that the noise is primarily from the transmission. I would think that this car would be more quiet. Any responses from owners with manual transmission would be appreciated.

Do you have the manual transmission? I have the S40 T5 Manual 2005 year. I have never heard this problem with transmission noise. The drivetrain is actually very quiet. However, if you still have the original Michelin Pilot tires the sound could be coming from the tires. These tires make a constant HUM sound that is more pronounced as the tires wear.