I noticed something similar in my engine at around the same mileage, maybe a little bit more. Usually it only happens when the engines cold, at least for me, i think its because the heads in these motors dont flow oil that great so it takes a sec for the oil to reach when u crank it.....i completely got rid of it by going to 10w. You might wanna try that, if it doesnt work, i used a quart of Marvel Mystery oil in my 300zx TT when it had a little bit of lifter tick, and it got rid of it completly. Hope this helps.
2002 FX4 Twin Sticks