ADAM31

I have a 2021 Specialized Tarmac 12 speed with SRAM Axis shifters, I have noticed that in the last 6-8 weeks more rattling coming from when I am in my big chain ring and either in the first two or last two gears. I have always road a 10 speed in the past so this is new experience riding the 12 speed, I am wondering is it normal after putting about 7000 miles on the bike that this rattling is normal. The rattling was not there in the first 5-6 months of riding in any gear that I noticed. Two different bike mechanics have looked at it and said everything seems good, they did a little adjustment on the limit screw but that’s about it. I should clarify sounds like more of rubbing sound on front derailleur cage

I thought initially I needed to change my cassette but we did that and it made no difference. I have kept up with changing out the chains on my third one since owning the bike and I clean the chain and cassette regularly.

Andrew R Stewart 

Der adjustments, worn rings, worn pulleys, bent stuff, loose stuff. Just some of the possible causes.

BTW- As the cogs and chains have gotten thinner their wear rates do increase as well as the consequences of poor condition (either wear or adjustment). We find that by the time the cassette sees 3 chains it's usually pretty worn too. Andy

CliffordK

Ok, so you've replaced a couple of chains. What brand? Quick Link?

Can you reproduce the problem on the repair stand, or is it only while riding?

Tight links in the chain can create some issues. Watch the chain as it feeds through the rear derailleur, either pedalling forward or back on the stand, or upside-down. Any hops in the derailleur.

You can also get creaks in either the bottom bracket, or in the crank spider. And, of course, in the seat.

DaveSSS 

SRAM AXS uses micro adjustments from the shift levers to center the travel of the RD. The limit screws should backed out slightly before changing the adjustment. When you're satisfied with the shifting, shift to the smallest and largest sprockets and turn each screw in until it barely touches. Sram has YouTube videos on all parts of the setup.

Most users are getting very long life from their AXS chains.
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Iride01 

So what does the dealer say about it? Certainly with a new bike you've taken it back to see if there are some issues that the dealer that put the bike together might should cover.