Tapping noise from 2.3 Cabriolet NG engine

Hi all, wonder if anyone can help, my 1993 Cabriolet has developed a " tapping " noise? If it gets revved over 2500/3000 RPM I can hear a really loud and annoying tapping noise, from what I think is the vacuum pump, any ideas anyone? Also she's VERY sluggish at low RPM, but if you throttle hard and go up through the gears it picks up really nicely- for a 23 year old Audi anyway- Also the oil pressure light comes on at higher RPM, have changed oil and filter, correct amount of oil in, changed the oil pressure switch, but still I get the light? Bad wiring?
Anyway, thanks in advance if anyone can help, would REALLY appreciate it,
cheers,
Steve