STOP oil pressure warning light.

I bought a 2005 Passat 1.8T, about 1 year ago with 40k. Ive
always changed the oil on time with full synthetic as
recommended, never beat it and have never been low on
oil. This light came on and then it started making a noise.
Not ticking, but I thought it was. I sea foamed it and drove it
for a bit for a week, used an engine flush, with an oil change  
and new filter and used injector cleaner. a mechanic looked
it it, and said it runs and sounds great.. except the warning
light (sound never happened again) but now it drives for
about 15 min, then the light comes on again. I have only
been running it to maybe clean the injectors and get more
gunk to collect in the oil filter... What should I do next? I
need this car.. thanks if anyone can help.