I am very sorry and surprised to read your experience.
I am very sad to receive such a bad review, especially because the problem you stated is an external factor and not a review on the house itself.
Most of all, I am surprised , as you haven't mentioned anything during your stay and by that way gave me the chance to assist and verify and as of the fact that the other guests that stayed in this house described it as silent and no one has yet experienced this kind of problem (you may notice all 5-star reviews, except yours).
anyway, there is no garage under the building.
What you're probably mentioning is the entrance gate with access to the basement, that is rarely fully opened (normally the small door is used).
Nevertheless, after your experience, since I am unable to exclude the improbable over exaggerated usage of gate doors by one of the tenants during holidays and during the night, as you stated, I went there this morning to verify.
The concierge lady (that you probably met and that could have assisted you as well) denied any exaggerated usage of the gate doors and was surprised to hear your experience. Especially during night.
We have tried to open and close the gate more times and I must say that I can not confirm that the sound is disturbing, anyway.
It is more probable that you are particularly sensitive person regarding any sounds.
Regardless of such different personal perception, I have informed the administration of the building and further measurements and improvements will be done, and the problem in case, will be solved.
What I disliked mostly is your opinion that nothing can be done. This is simply not true. The apartment is situated in the city center of Milan and in case of disturbing noises building administration is obliged by law to reduce them.
I also disliked you not mentioning this problem during stay so that I could have assisted and verified together with you. Our business is small family business and this mean review can seriously affect it and is really not kind and friendly.