To be fair, not all high-end speakers work with all high-end amplifiers.  The Sonos amp-and-speaker units such as the Play:5 and One are ones that Sonos can control and match, though room acoustics also play a part. 
 

That may not address your specific point about the Connect Amp with your choice of speakers, but if you have access to any other speakers, why not try them and see how they sound?

I have an Ecler IC8, and they also sound better with the old receiver. And they are much cheaper than Monitor Audio. And they play with the same metallic sound with Sonos Connect Amp. In this discussion, sir hears a similar sound  with new Sonos Amp: https://en.community.sonos.com/components-228996/amp-so-stoked-but-underwelmed-by-sound-quality-6847304
I live in Russia in a small town, I don't have the opportunity to check the device before buying.

Hi @artem.  

Thank you for reaching out and welcome to the Sonos Community. I appreciate for bringing your concern to us and letting us know about it. Let me help you figure out what's happening.

First I'd like to isolate the issue so we can create a path towards resolution.

1. When did the issue start happening?
2. Have you noticed any difference in audio quality when your Sonos Connect Amp connected to your WiFi or wired to your router?
3. How do you use your Sonos Connect Amp? What are the devices connected to it?
4. How is your receiver connected to Sonos?
5. Do you experience the same issue from certain music sources? 

I'd appreciate it if you can submit a diagnostic report from your Sonos system to check what's going on.

If you need help with any other information, please be sure to let us know.

The Sonos Community is always here to help.

1. Immediately after the first turn on (and now after 100 hours of listening), I hear a sharp metallic sound (with sibilants sss ssss, and expressionless low frequencies).
2. There is no difference.
3. Only connected 2 speaker Monitor Audio CP-CT380.
4. My receiver is not connected to Sonos Connect Amp in any way. Only Connect Amp + Monitor Audio CP-CT380. I listen to Apple Music, Spotify and from HDD. But I had the idea to check with an old and cheap Yamaha RX-V363, which is made for movies, not for music like Sonos (I thought Sonos is for music). But it turned out that the old Yamaha is more musical and softer. I also plugged in my old cheap Ecler IC8, and they sound worse with Sonos.
5. I have never had a device of this level with such a bad sound.

Hi @artem. Thank you for your response. I appreciate you answering all my questions and providing the details of the issue as well as the steps that you have performed. I’m sorry to hear that you’re experiencing this with your Sonos Connect Amp.

I would like to suggest the following steps to check if this would help out.

Before you proceed, please submit a diagnostic report to get a snapshot of your system.

1. Power off your Connect Amp.
2. Disconnect the left channel speakers and play music to test if you’re getting the same sharp metallic sound.
3. Disconnect the right channel speakers and connect your left channel speakers. Play music to test.

If you’re still experiencing the same sound quality, power off your Connect Amp, disconnect your speakers, and power it back up.

Run another submit a diagnostic to compare the report from the first one and for us to check what’s going on to further help you with this.

We're here to answer any further questions you have. You're always welcome here in the community.

But hopefully you can change it if defective because having used two Connect Amps since 2012, I can't see this kind of behaviour happen from a unit that isn't defective in some way. And my Connect amps replaced HiFi amps, and are wired to the same HiFi speakers with no difference in sound quality after the replacement.

Hi, @Rowena B.  Thank you for these solutions.

1. It turns off every night. And, in addition, I turned it off many times for testing.

2. I tried different options and other audio cable.

3. I tried connecting 2 and 4 audio speakers.

4.  diagnostic is:1029931112
   
    

   
   I live in Russia in a small town, I don't have the opportunity to check the device before buying.

   But hopefully you can change it if defective because having used two Connect Amps since 2012, I can't see this kind of behaviour happen from a unit that isn't defective in some way. And my Connect amps replaced HiFi amps, and are wired to the same HiFi speakers with no difference in sound quality after the replacement.

    

   Hi, @Kumar . Thank you for your response.

   It is very strange that you do not hear the difference between different devices, because each has its own sound. Each DAC and each amplifier has a different sound. Even every OpAmp sounds so different...

   Unfortunately, I can't rent it out or change it for another one. The only option I'm considering is selling this for at least some money and buying a higher-end device, but I really wanted to stay in the same ecosystem with my other Sonos devices. I don't think there's a problem with it anymore. It just sounds that way.

It is very strange that you hear differences because all solid state amps of the same measured spec for power and THD sound the same when played into the same speakers, unless they are defective or perhaps cheap Chinese ones - no one has been able to pick the difference, ever, anywhere in the world, in a strict level matched double blind test between two amps of the same power spec and THD level coming from any well known brand. Ditto for DACs of the same measure relevant specs. 

But this is an old old story.

Since you do hear the differences I suppose you will have to learn to live with the:  it just sounds that way. It is the price to pay for having golden ears.

Perhaps the amp has to just burn in?:-)

@Kumar, you probably mean that there is no difference between the same models (the same company). And the new Sonos Amp model (not Connect Amp) sounds different. This is what users and reviewers say. If everything was so simple, then everyone would use the simplest amplifiers, would not spend money on Hi-End. I was surprised by your words that you didn't feel the difference with the old Hi-End amp, which just physically can't sound the same with the Sonos Connect Amp. About blind tests: when people distinguish the sound of the cable - Yes, I don't really believe in this. But every time I bought a new DAC, I heard a difference in sound: Asus Essence One, Sennheiser HDVD 800 and others.

I created this discussion just to fix a possible problem. Starting with Play 5, I bought Sonos devices (One SL, Beam, Arc) and did not think that I might not like the sound. Everything was always great. And there was no need to buy something more expensive. From the very first day of use, I recommended Sonos to my friends.

No, I meant between models from different companies.

And I gave up believing in what reviewers write, many years ago. I prefer to trust my ears. And my ears tell me that my two Connect Amps sound exactly the same as half a dozen amps I have used for the last twenty years, made by half a dozen famous HiFi brands. Some of these amps cost four times as much as the Connect Amp. The sound is exactly the same as long as the same speakers are used, placed in the same place in the same room. And so long as these speakers do not need more power than what the Connect Amp can deliver.

What the amps looks like only has a psychological effect which is why comparison tests have to be blind. Among other scientific criteria for such tests to be objectively valid. 

Does the Sonos amp sound different? I have no idea, I have not heard it. But all my experience tells me to not trust reviewers in HiFi magazines who do not do anything close to controlled blind tests before they talk about differences. So the odds are on it also sounding the same.

@Rowena B.  

Perhaps it is possible to manually lower the frequency near 7 kHz?

Hi folks.

Thank you for reaching out to the Sonos Community.

@Kumar, thank you for sharing your thoughts and experiences on this thread. 

@artem, I really appreciate your effort in performing the steps and for submitting the report.

Upon checking the diagnostic, I don't see any error that may cause the sharp metallic sound on your Sonos Connect Amp. 

About your comment above, do you mean changing the frequency on the Sonos app or are you referring to a different device?

In the Sonos app, you can check the EQ to adjust the bass and treble of your Sonos Connect Amp to check if you will hear any difference.

If you're still getting the same sound quality, the next step is to factory reset your Sonos Connect Amp. You may check this article reset your Sonos product to guide you.

Set up your Sonos Connect Amp after the factory reset. If the sound quality will not improve, I recommend contacting our Sonos Customer Care to further assist you with this.

If you need help with any other information, please be sure to let us know.

Hello, my friends! The problem with my Sonos Connect amp was solved by replacing the old cables with new ones to the speakers, surprisingly. Now the sound is all right. Thank you all and sorry for the negative messages. Have a nice day!

Hi @artem, thank you for the update. I'm glad that the issue with your Sonos Connect has been resolved.

If you need assistance with your Sonos or other information, please feel free to let us know.

We're here to answer any further questions you have.