had the same problem. it started happening when my rig had about 100000 km on the clock (got 150 now) - it was worse on cold start - the noise lasted for about 4 minutes until the oil reached working temp.

i tried an oil additive that worked really well - its made by an american company called BG. this is the additive:

http://www.bgprod.com/products/engineoil.html

I usually change the oil every 5000 km (its not something that the factory recomends but i like to keep the oil fresh) and i have added that stuff last 3 oil changes. works well.

2001 sporty. 4 inch lift+ body lift-front lovlells coils+extended forks. reat tj. monroe shocks. full skid plate, auxilary fan. external oil cooler. maxxis 8060 235/75 R15 tires on american racing wheels. trackfinder rear diff lock.
http://www.cardomain.com/ride/3948684/2001-kia-sportage