Impala ss 100000 miles. no power loss. The sound does have a rhythm to it but barely heard from a 5 feet from car. The sound does go away when brought to more than an idle. no check engine light. I have kept up with oil changes and check oil on fill up. I've own car for 6 months bought it with around 95000 on it. im worried it might be a lifter but does not as loud or change rhythm with rev. i just want to know if i should be concerned.