hi everyone. i am new to this porsche world.

i bought a 06 cayman s.
great car to drive.

however, my car sounds strange at around 1800-2000rpm. going around 65-70km/h

as if someone extra gas being stepped on. making this strange 200-300rpm increase at a sudden.

it sounded like ahhhhhh for 1 sec.
if i keep at constant spped say 70km/h constant rpm at 2000rpm.
it repeats this extra gas and increase 200-300rpm and drop back to 2000rpm

almost every 8 seconds interval it did the same.

can anyone suggest what might be the problem???