Pressure Release After Engine turn off
I am currently driving a 2006 IS350. Usually after turning off the engine, there seem be a smooth pressure releasing sound near the back the engine. I assume it is the exhaust gas or something related. Anyways, for the past couple days, after i turned off the engine, the pressure releasing sound becomes pulsed (pressure releasing sound, stops, pressure releasing sound again, stops again, and repeat). This is occuring after the valve spring recall and I am wondering if this recall or cold temperature, 6 degree celcius, can be the reason. And is it harmful to the engine?
thanks for your advises