rattle, when warmed up, is telling you that BMEP (cylinder pressure) at TDC is climbing very high. Overtiming. It is stressful and costly over time, and not worth the extra 1/2 mpg. There have been products rushed to market. i would err on caution, and settle for the tune that doesn't rattle, all else being the same. Leave rattle for those who can monitor the timing changes. That's my opinion.