There is a utube video listed under (1999 911 996 3.4 engine noise) by Andy Jackson. This is exactly what my car sounds like but he said it was his water pump and fixed the problem but I don't think I have a water pump on my car.
My car has 96000 miles.
My car has a manual transmission.
I would have to listen to the noise firsthand to know for certain. However, one guess is that the noise you’re hearing is from the valvetrain. Valvetrain noise, such as worn lifters or misadjusted valve clearance, is generally characterized by a light clicking or tapping sound from the upper portion of the engine. This noise has a frequency half that of engine speed. The noise could also be an exhaust leak. I recommend having a professional diagnose your engine noise in person. The team at YourMechanic is an excellent option.
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