I recently purchased a 2007 328 xi with 24,000 miles. This is the first BMW I have had in years. I can't tell you how nice it is to be back in a BMW again. I really missed the drive. I have had the car for about three weeks now and the other day I noticed a knocking noise coming from the engine when it first started up in the morning. After about 10 minutes of driving the noise went away. However the noise came back once the car sat overnight and completely off again. The sound is a little like the sound a car makes when the oil level is low (valves knocking) but I checked the oil level and it is full. I was wondering if anyone had an idea what may be causing the noise and wat needs to be done to correct te problem?