It COULD be a lot of things. It is easiest to start with the simple and do an oil change, which it sounds like it needs anyway. If you still have noise, then you can get paranoid. I would recommend not getting paranoid too soon. BTDT. 
If there is one thing that I have learned over the years, it is that you fix what you know is a problem first. It is sometimes surprising how things that you might not think are related actually are.
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'03 S, manual, 18" Carrera wheels, PSM, PSE, Litronic, 996 Cluster, +
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