The Stuttgart-based company said in a statement that the 18 627 cars being recalled are part of the 911 Carrera S and 911 Carrera 4S lines and were produced between April 2004 and October 2005.
Porsche said the welding seams on the exhaust pipe could weaken, causing it to ultimately fall off. The company said there were about 30 known cases of that happening, but that there were no injuries reported.
The 911 Carrera 4S manual retails for around R1.02m.
The company's cars come in four different models, including the Boxster, the 911 series, the Cayenne sport utility vehicle and the Carrera GT.
Despite the recall, shares of Porsche gained 1.5% in Frankfurt trading.