I recently had mine installed indoors and regret it.

It's not so much the noise, it's the vibration. The damn thing reverberates through the whole house. In some areas it's quiet, in other areas there's a very disruptive hum.

The worst part though? It has an app which is infuriatingly shit. None of it makes sense, and much of it is silently locked down without informing the user (get used to "Oops! Try again!" messages).

There is no way to shut it up during sleeping hours. I cannot believe there is no option to do so. If I had kids trying to sleep here, I would demand a refund for this reason alone. It is marketed as a super quiet heat pump for indoor installation.

The firmware is cooked. Sometimes the compressor just stays on... I've left it for 36hrs+ and it never turns off. I have to power cycle it.

Fortunately there is an option in the app to use the backup electric heater instead of the heat pump. I'm willing to just use it as a poor electric heater at this point. But... It's broken. It just silently doesn't take effect. Literally as I'm typing this, the room is vibrating due to the compressor while the app reports the electric heater is off.

And now I'm mad again. Fuck Stiebel Eltron.

I've never used a Steibel Eltron tank heater (but have owned their tankless), but neither the AOSmith nor Rheem require an app to use. Both can be placed into "Electric Only" mode via front control buttons == no noise.

The Rheem specifically has a time-of-use relay/powerbox, so you can put a timer onto it which will interrupt ALL heating with a rotary dial/timer. This is entirely mechanical, without computer/app.

Sounds like your unit is cooked (36 hours continues heatpump is very bad for the pump).