I have a 1996 VW Passat V6. Had everything replaced, Oil gasket replaced between oil housing, replaced the oil sensor, oil filter and changed oil. For one I would Never add a oil additive there just bad noise. I had a VW mechanic tell me its the oil screen in the oil pan that needs clean, Im going to clean it this week end but the new gasket is about 36 bucks. Im also going to check the wires going to the sensor for correct placement. My alarm goes off after 2000 rpm and never goes off till we are at desto.
Hope this might help.