The CX3,5, M3 had a spring protector TSB for the random intermittent clunk. The 9 came much later & may not be included in the dated advisory. Try asking your dealerships. The OEM protector is cheap.
Hope that forum gets revived. The wealth of info there should be shared.
On CAI, have you seen AEM's 2.0 MT specific one?
https://www.aemintakes.com/mobile/product.aspx?prod=21-765C
Nah, that's a borrowed 1.5 SkyG head off a salvage yard for port templating. Still on the lookout for a 2.0 & 2.5. The Sky-specific walnut blast procedure won't need engine nor head removal, of course.:)