Thanks Johnny!
I compared to my friend Speed version and the exhaust systems look identical and since mine was imported from US, it has #20 setup.

I'm the 2nd owner, the 1st owner bought it used from US and he said he didn't do any modification. So if the exhaust was modified, it could be done in the US, before shipping to Vietnam.

So I don't know what makes the sound different on my friend Speed ver and mine. Do you think I got malfunction flap / valve / vacuum or software control?

 

I believe that your flaps are working fine, as you have said that on cold start they are open, then when warm they close, do you hear any difference from cold to warm upon start up, meaning, loud to not as loud ?

Next, you say that they look identical, but yours is imported from the USA, is your friend's also imported from the USA, or are you confusing your system with just 2 CATS, with his system with just 2 mufflers, as if he has mufflers instead of secondary cats, his will be quieter.

Johnny

 

On cold start the flap is open and the sound is very loud as the RPM is also high. Then the RPM drop to 500 and the sound gets not to loud, a bit quieter, and the flap is close.

The drone sound is loud when you drive at low speed, especially when you release the gas pedal.

I forgot to aks, but I think my friend Speed car was also US imported. I will double check with him tomorrow as it's 1am here

Here are the photos he sent me, I find it's pretty much the same as mine, what do you think ?

 

I know him.... LOL
Yes, they look the same, he has two CATS there, next would be to drop your pipes to see if the owner in the US gutted the secondary cats as they are not need to pass emissions..

Get some sleep, talk tomorrow.

Johnny

 

My friend confirmed his Speed was imported from US, too. So basically his exhaust and mine should be the same, right?

I will check on mine to see whether the secondary cats still there 😁😁😁 but do you think this part help to reduce the sound?

Many thanks

 

Today I have a chance to take photo of my exhaust again. I also check the flap and it opens all the time now. I guess there is something wrong with the flap. My BMW 760Li has the flap close most of the time, and open only on sport mode with hard acceleration.

 

I am thinking about adding the resonator right after the 2nd cats, just like the GT setup. What do you think? I asked an tech at the pipe shop today and he said it might help to reduce the drone sound.