I have an email from randy stating that they saw some interference as a result of the change in vibration frequencies caused by non stock RMM's. He didn't mention Cobb's specifically, I just mentioned that I was planning on getting one. I'm sure there's something to it and considering Mountune is developing parts which uphold the factory warranty they can't supply parts that may have this type of effect. I'm sure whatever effect it might have is totally unnoticeable to the person driving as the computer will deal with it, but any potential for excess knock or pulling of timing to handle it would effect performance and reliability... Two things any manufacturer wants to avoid.