A3 oil light and engine noise
 

I own a 2005 2 T A3 which have the following problem:
Engine make a noise when starting which clears within a few seconds. This has been occuring for months.
The noise sounded innitially like the starter motor was stuck.
The oil light started flickering yesterday when the rpm higher than 1500, flickering, which according to the manual is a faulty switch. The oil level was very low so I topped it up but the light remained on.
The noise after starting is now worse since the oil light came on.
I have read the othe rcomments about similiar problems and will check what they suggested.
Any suggestions would be welcome