Oil light coming on constantly!
 

I just bought my 9-3 in december and its ran beautiful, but just recently in february something happened, I dont kno wen it was caused it jus happened like literally at a moments notice. My engine started running kind of raspy, sort of like its out of oil but i had a fresh oil change along with filter. My oil light comes on after running it for awhile and while Im idling. I have jus bought a motor flush and was told to run 30 weight oil for 100 miles afterwards. It is still sounding weird, like a raspy, winding noise. Has anyone had a problem before? Any suggestions?