Ls3 startup rattle

[Mik 030]

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???

 

[VXBaz]

What ended up happening Mik?

 

[Mik 030]

Thanks for a response. Started it the following morning, still loud rattle. Turned it off and swapped accelerator pedal. Restarted with less rattle, but still worrying. As I went to press the stop button, the rattle faded and over 30 seconds, became a standard idle. I gave it a slow 5 min drive with no revving. All appeared ok. Did the pedal swap again (to the sports pedal). Started ok. On the next morning, I started the car with some apprehension, but all was perfect and continues to be it's usual satisfying startup with no untoward rattles, etc.
This all sounds crazy, ie linking the pedal start to the rattle, but it was the only clue I had.
Have a vid of the less harsh startup rattle. So, touch wood, I won't hear that sound again. Love the car. Tows an Ecotourer van effortlessly.

 

[VXBaz]

Very strange. As a new LS3 owner I was interested to hear what was going on. Wish I could help but I'll step back from offering any suggestions. I hope someone can shed some light on this because that certainly is weird.