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.
Engine pinging/rattling on acceleration. Sounds like valve/lifter rattle. Not very loud but I can still hear it. More so under hard acceleration. When I had it at Christian Brothers awhile back they wanted to do an injector cleaning but I passed. I've cleaned MAF sensor and the oil is fairly fresh.