Did you ever get an answer on this?
I have the same thing and everyone just says the B58 is known to be loud, but for it to come through the cabin is definitely annoying.
2026 MT with 1200 miles.
I just noticed this annoying “woodpecker” noise during idle. After testing some more today, I realized the noise is most consistent after cold start once the cats warm up but car is still not at operating temp. Increasing RMPs even a tiny amount causes it to go away but...