Honestly OP, they're actually doing you a favour in the long run.
If you continue trying to make the world 'quiet' so your DC can sleep, then you're actually making both your DC's and your own lives harder, because the whole damn world is 'noisy', and being able to 'tune it out' while sleeping is actually the best thing you can teach your DC for their future.
I've had friends who did the whole 'we all need to be quiet cos DC is sleeping' thing, and they suffered for it. They couldn't have friends round or even a dinner party, even once their kids were older, because the kids would keep getting up because they couldn't sleep through the 'noise' of anyone else in the house ffs !
For decades, they tip-toed around every damn night ! That's NO way to live !
I deliberately NEVER made anything 'quiet' for my kids, and as a result, they can both sleep through anything !
If your DC can only drop off and then stay asleep if it's quiet, then they'll never be able to;
Live in a city, cos they're damn well 'noisy' 24 hrs a day in some places.
Live with a partner who snores/works shifts/insomniac etc.
Be able to sleep in hotels/ on holiday etc.
Sleep while travelling e.g on a plane/bus/train.
Cope with their own DC crying at night etc
Take a deep breath, and carry on, and remember, they're actually doing you a favour (even if it doesn't seem like it right now). You and your DP will get your own place eventually, and all this will simply become a memory.