Non-Bose system. Upgraded Alpine Component speakers in the front only. 2018 Mazda 3, but most Mazda's have been using this TAU (Tuner Amplifier Unit) for over a decade now.

Even with the car off, in accessory mode, once the infotainment system boots up, a high frequency (10kHz) hiss appears. It is very faint, however after adding an external amp to the system the hiss is more pronounced and noticeable, even when driving and all sound muted. Using a phone spectrum analyzer, the hiss is a 20db spike above background noise at exactly 10kHz, and only 10kHz. Without the amp connected it is only a 6db spike, so it is clear the hiss is from the TAU and not the amp. Note that the hiss is there even when the audio is paused, volume at zero or muted. Unfortunately, you can't turn off the Mazda audio system.

I wanted confirmation if others have this condition (this way, the system is just poorly designed, I will just live with it).
Does anyone have an idea to solve it?

It is unlikely anyone will hear or notice this with the stock tweets, for they are near useless and do not even reproduce 10kHz frequency. The issue would be noticeable with upgraded speakers and/or secondary amp.

 

The vast majority of new car buyers stick with the stock system so it may be difficult to find others who have experienced the problem if it is not noticeable with the stock speakers. If you have the equipment to detect and quantify the problem where average drivers might not, you may want to go to a dealership and see if the problem is on a few cars on the lot.

Is it true that you have been a member for 11 years and this is your first post? If so a belated welcome to the forum - it is good to hear from you.

 

I'm back to owning a Mazda from a 6 year Prius sabbatical. My previous Mazda's were the 3 and RX8. Sadly, Mazda has not fixed many of the issues that plagued the 3 from 14 years ago. Too much selling the sizzle and not enough substance. They tout the new and improved Skyactive system, yet MPG and ponies have changed little. The G-force system is hype as well, as detailed testing confirms. The car still lacks adjustable rear camber; once driven off the showroom floor it begins a journey of poor tire wear. It's not all bad, for the car behaves solid and reassuring (as did previous versions), and is definitely fun to drive. I guess I just set my expectations too high.

In previous years, I found most of my answers without needing to post questions, however this issue, and moreover after much searching I found many have had this problem, yet know one has a successful solution. The hiss spike at 10kHz might trigger some expertise on a solution, or at least a cause other than poor amplifier design. It could very well be intentional by Mazda to prevent better and less costly aftermarket systems that push buyers into the expensive and mediocre Bose factory system. I hope some one chimes in with new insights.

Aside Mazda's shortcomings, it is nice to be back.

 

If your aftermarket amp isn't connected, how on earth are you getting anything thru the speakers? I would be checking your wiring.

 

I added a male/female connector for the speaker wiring to the external amp under the dash just below the steering column. I use a return plug that sends the signal back to disable the external amp. This way, I can isolate a problem should the amp fail.

This audio connector location is excellent for a crossover connection for component speakers. This way, there is no breach of the factory wiring harness into the doors, as many attempt to mount the crossover to the door. Access to the area is a bit cramped though. Connector is C-35 where the output from the factory amp connects to the front door and dash speaker, both left and right are at the same connector. Unplug the car battery and use a test signal to determine if the wire comes from the amp or which speaker it goes to, for all 3 wires are the same color without specific identification. Don't remove the C-35 connector, for the yellow and violet wires are power leads to other circuits in the car.

 

Is it true that you have been a member for 11 years and this is your first post?

 

Yes. I joined when I owned a 2006 RX8 and 2007 Mazda 3 hatchback. Most times I can find my answers, so no need to post. I thought others in the forum may have a clue. Further analysis uncovered the Alpine crossover is poorly engineered, so tweaking both the woofer and tweeter crossovers, I was able to minimize the issue and create a smoother better frequency curve. The system blows the doors off any factory Mazda 3 system for just a few hundred bucks. I also added a sub under the seat. The 10k hiss is still there, but livable.