I don't know why it does that... ?
But, mine does the same thing! I have about 85k miles now. I was told to go to a thicker oil and that should help. have been scared to do it though untill I hear if others have tried it yet. My only mod is Flowmaster 40's and deleted resonators. STOCK otherwise. I have been afaid to do much to it for fear of tearing it up. ( HAD BAD LUCK WITH MY OTHERS - NOS BAD..uummmK! ) so far no major problems. Just normal upkeep,brakes, rotors, hubs, oils changes. I plan to mod AFTER its paid for...not before!
Interested to hear the comments on this issue though! I was told to go to a full synthetic 10w-40, or a 20w-40.