It does it all the time, although it is louder when driving vs in park. A friend said it may be the exhaust manifold gasket, no smoke out the tail pipe.
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1996 Mercury Sable Question: What is causing a ticking, tapping or seems almost like vacumn leak.
Answer #1Convoy Auto Repair & Towing (38 Answers) , San Diego, CA - (858) 560-9131ConvoyAuto July 01, 2011, 09:21Technician
It may likely be an exhaust manifold and/or gasket leak. We have special equipment that can pinpoint the source of the noise. If it is an exhaust leak, left unrepaired it may do damage to the oxygen sensor and valves.