[Simons975]

I have always thought, and heard that the exhaust valve opens at cold start and the closes at normal driving. However that not the case, at least not with my car.
It started with that I had a M performance exhaust installed. I didn't like the sound when I started the car in the morning. It was waking up all the neighbors. So, I put my hand behind the exhaust pipes at a cold start. The valve was closed!
With the valve closed the engine works with higher pressure and gets warmer faster. With all the exhaust air running through one pipe and with higher pressure, it sounds more. After a while the engine got warmer and the valve opened and... it was less sound!
Now I have removed the sprint to the valve and fixed it in open position. So now the cold starts are not that loud.

[Buckeyes]

The loud cold start is from the wastegate full open. The exhaust flap, open or closed, doesn't make much difference with regards to cold starts. I have the mpe and a catless downpipe. Talk about a noisy 30 seconds. A cold start with the mpe is like a church mouse compared too a downpipe.

[Project Elite]

I've had experience with catless dp and mpe as well. Terrible cold start but that goes for any exhaust on these cars... I've noticed that the colder it is, the louder the cold start as it will choke the idle at a higher rev to stay warm.