The most likely cause is lash adjuster noise. As the engine sits overnight, the oil drains back to the oilpan. Of course, first thing in the morning with the oil being thicker, it takes a little while for the lash adjusters to pump up with oil. It is normal on many cars, including my C240. The only time you should be concerned about it is if it doesn't go away. If it doesn't go away, the most likely cause is low oil level or bad adjusters.
what car/engine is this in? sounds like lifter ticking/tapping. once engine warms up the clearances fine and the lifter gets enough oil pressure. Or the secondary air injection turning on which makes a "dieseling" type noise which is normal for the newer vehicles
My wife's car had a similar problem but it only happened once for some reason. Don't know if that was related to cold weather (we always kept the car in the garage though)...anyway, I did notice that we need to add 1.5 qt of oil as the oil level seems to be running low. We just did service B which includes changing oil, but I don't know what type of oil the mechanic changed (I think it's Mobil 1, but not sure if it's 5W40 or something else). If I go buy some Mobil 1 oil can I just top it off? Does it matter to mix two different ratings of engine oil (as long as they are both Mobil 1 synthetic)?? For colder weather what ratings of oil should I use? Thanks!
My SLK 2005 had the problem few years back, was one of the pulley, replaced and the clicking stopped for few years till few mont go. Bring the car in the shop 2 more times kept overnite, replace other parts but not the clicking noise, they told me they don't hear any noise at start at all. Bring my car home, start my car the next morning the noise still there. I have notice the noice only on a moist or rainy day. total bill 1700 $, problem not solved.
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