Purchased my 3rd Mazda , first skyactive engine. My 2022 CX-5 CE non turbo drives great - but unlike my 2010 3 has the skyactive 2.5 engine. I only have 800 miles on it .
My question to other CX5 owners is about cold starts - I noticed a ratting noise when in the cold am I start up . It lasts less than 30 seconds and like clockwork stops rattling . It sounds like a catalytic converter . So I called a few service depts instead of following the regular advice " bring it in and make an appointment " . I finally found a few advisors that said its normal and they hear it on every cold 5 - It does not do this once warmed up or on warm restarts . I then found a guy who explained , its again normal and whats occuring is the timing is being retarded in order. to have the detonation occur further down the exhaust closer to the cat to reduce start up emissions and warm the cat . Sounds plausable , and most might not notice it with the door closed as the car is well insulated . It does it every morning and its often 30-40 degrees where I live . It also appears to be timed and consistent , as it shuts off like its intentional - anyone else notice the start up rattling - ? Not refering to the high pitched clicking the fuel pump makes - That is one I know is a design characteristic of the pump - Dont get any codes and it drives great- just figure it had only 2 miles on it when I took it and it came straight from HOFU Japan . No demos . I would find it hard to believe that it came off the line in Japan with a defect in workmanship -
Thnx fellow Mazda owners - ps - Still have my 2010 Mazda 3 , 2.5 with 145k and could not bear to let it go on a trade in -

 

Its the flame front of the combustion leaving the cylinder and heading towards the catalytic convertor to help warm it up quick to reduce emissions.

 

Its normal, if you watch your Tachometer the sounds should reduce when the RPM drop at or below 1000 after starting up. This is the ECU adjusting and the engine going into what's called closed loop. The rest of the explanation is what Grim posted.

 

Thanks for the feedback Grim : Calli - Ive had several non-skyactive Mazdas and still have my 2010 2.5 /3
None had the "cat ratlle" - I have now dubbed it - But it appears to be consistent throughout the syactive platform for years - It dosent bother me as long as its intentional- You are correct , it goes away relatively fast and does not return during normal stop start driving after inital cold start -Suspect most people dont even listen to the engine and have the doors closed / in which case it is never detected by less type A Mazda owners who are listening to music or talking on the phone - Thnx Again !!!!
Found this guy who isolated its cause as well

https://duckduckgo.com/?q=New+mazda+...%3DcdjIF4jYQow

 

Normal as noted.