I second the playing of solitude type music ... aka instrumental no words ... played loudly enough that it provides the 'consistent noise' in the house and mid sleep cycle noise just becomes background noise as part of the music.

This works awesome for me my crew have all consistently slept 2.5 - 3 hours and I never have an issue when a newbie starts with them hearing them and waking up if they are having adjustment issues.

I just transitioned in a horrible sleeper myself this past spring .... mom had to start a job 4 months earlier than anticipated and had not had time to prepare him for group care but despite his issues everyone else was sleeping through it ~ just him and myself who were exhausted those first few days and now he too sleeps 3 hours plus in the afternoon on his own without issue ... consistent expectations that it was time for him to sleep and when he would wake mid sleep cycle I would help show him how to soothe back to sleep again and than weaned back with that support once he was sleeping 3 hours so that he needed less and less assistance with self soothing and now at 14 months climbs onto his cot by himself and goes to sleep unassisted ~ never was able to get him into a crib swear he has claustrophobia cause he hates confined spaces!