Hello, I appreciate any advice with this problem I've been having. I purchased a 2001 Infiniti QX4 (same engine as a 2001 Nissan Pathfinder) on 07/05/2014 from a local used car dealership. At the time of purchase, I noticed the vehicle had a loud start. I checked the oil and found it was about quart low. I bought the car with the promise to fix any oil leaks; fortunately, there were none and the car just was low. Since I've owned the car, I've noticed a consistent problem. Every time I start the car first thing in the morning, or anytime it has been sitting for a longtime (maybe 6+ hours) there is a loud start (loud rattle noise) for a few seconds then goes away. No matter how many times I start it the rest of the day, there isn't anymore problems unless it sits for a while. I was hopeful that an oil change would have fixed this. I changed the oil to Mobil 1 High Mileage 5w30 Full synthetic with a new filter (Purolater) and the problem still exists? It has been approx. 1200 miles since I changed the oil. Any ideas of what can fix this? I'm hoping it isn't serious. The truck is good shape other than this. Should I change the oil frequently for a while? I also considered a flush to help clear out any sludge, but I'm hesitant. Quick Overview: 2001 Infiniti QX4 Currently running Mobil 1 High Mileage 5w30 Full Synthetic (Is this great to run?) Purolater Oil Filter LOUD rattle noise on cold start for a few seconds Noise doesn't happen unless vehicle sits for a while. Unknown maintenance history/ Possible neglect (carfax shows vehicle was a lease for 9 years and 2 owners owning for a short amount of time) and vehicle was 1 quart low at time of purchase Quick history, Owner 1: Lease 9 years, Owner 2: Owned 2 years, Owner 3: Owned 2 years, Owner 4: Me Owner's Manual calls for: -5w30 SAE -API Certification Mark -API Grade SG/SH, Energy Conserving I & II or API Grade SJ, Energy Conserving -ILSAC grade GF-1 & GF-I I appreciate any help! Thank You!