Did the sports pedal swap on my 2016 Calais. Started it a day later and heard a loud consistent rattle from the top end. Stopped it immediately and did an under bonnet check. No oil issues. All looked normal. May have detected an odd smell, perhaps electrical or not. When I parked it in the garage on it's previous trip, all was normal. I did a second start and heard the same sound. Hard clatter, so shut down. Had many ks with LS1 and know the lifter rattle. This sounds sharper and louder. Has had no hard revving in the last trip. Hard to believe ther is a connection between the pedal change and the engine noise. Don't want to do a third start until I have some advice. Any ideas???