4 cylinders are usually a bit louder. I have a question, do you drive the car daily?? Or every other day?? If I let my '92 400SE sits for couple days, the first 10 min will be very loud(sounds like a Turbo Desiel in Dodge Rams), and then it quiets down.
If it quiets down after the engine warms up, there should be nothing to worry about. Because the car sits over night, and gravity will pull the oil down. When you started the engine, pump will pump the oil back up, and during that time(that's why most tech will tell you that the engine wears the most when starting up), louder sound(valves) is expected.
Anyone has different view?? I am here to learn