You may be surprÂ­ised to discover that a carbon monoxide (CO) detector really isn't a complicated piece of equipment. Housed inside a plastic chamber approximately 3 inches (7.6 centimeters) in diameter are parts that work in unison to alert a househoÂ­ld when lethal gas is detected.
This type of noise is usually caused by malfunctioning valve lifters or an exhaust manifold leak. If the noise lasts for more than a minute and completely disappears or dimishes after the engine is warm, the most likely cause is an exhaust manifold leak.
(with a V8 engine and AFM (RPO Codes L76, LC9, LFA, LH6, LMG, LS4 and LYS) If an AFM lifter unlocks as soon as the engine is started, a SES light and DTC P0300 will be experienced with engine misfires on cylinder 1, 4, 6 or 7 but it is unlikely that any noise will be experienced.