Tim Pryor

Yes, the fuse was behind the panel in the trunk, second from the bottom slot.
Your problem didn't sound exactly the same but thought maybe the amp reset would help.

for kurtatx:
My S4 is having the B&O trim peel off the speakers in the door. Amazing car but I don't anticipate these kind of issues.

Audi issued a recall for the speaker trim:
https://static.nhtsa.gov/odi/rcl/201...7V675-1270.pdf
(Note the S4s are considered A4s on a lot of things so the S4 is also affected by it even though it just says 'A4 and Allroad' The S4 is considered a 'trim' of A4)

kurtatx

Thank you, sir. Looks like mine were done but it has happened again. No big deal.

TT-S4

The dealer techs could not "duplicate" the sub failure.
They had my S4 for 2 days, and they said that every time they started the car the sub worked every time.
When I picked it up last night the sub came on as it should.

I'm now starting to think that the fuse reset may have actually corrected the issue.
THANK YOU, Tim.

After I did the fuse reset I posted that the sub didn't come on the next day after work.
It worked the next morning, and when I got in after work the sub did not come on.
However, it was on Sat radio, and when I switched it to FM-HD the sub came on.
Odd indeed.
I took the car in the next day, so not much testing time after that reset.

Anyway, update on what they did to improve the sub.
They discovered the the protective "cage" around the sub was lose, so they added some felt in some areas and tightened down the cage.
Also, they found that the third brake light was very loose and buzzing.
That assembly can not be tightened, so they ordered and installed a new light.

When I picked up my S4 last night the sub was noticeably not rattling and buzzing the way it was before.
VERY NICE!
Seems the two things they corrected really helped.
To get some buzzing now I have to crank the sub level to max, and turn the bass level up passed 4 o'clock position and play music that has a lot of bass and sub.
But, those are extreme settings, and still any buzzing is now very slight.

I run the sub level once notch above the noon position, and the bass level about 2-3 notches above noon.
Overall, the system sounds much better as the sub rattle and buzzing is gone.

I'm happy now with the B&O audio.
As long as the sub keeps coming on every time, and the buzzing and rattling stay away, that will be great.

Void20

This. Have you managed to find a way to disable noise cancelation? I feel the same, that sound is being altered while moving compared to when stationary.

Also, how is the subwoofer performance now after a period of time? rattle free?

bruce_miranda

Sound dependent volume can impact the tonal quality. Turn it down to the minimum. It's a pity it cannot be turned off.