We stayed at Petit Hotel November 2023 and yes, the noise comes principally from Rainbow, they have speakers the size of fridge blasting out. It is audible even at Petit Hotel. IIRC was worst at weekends. The rocks in front of Petit Hotel aren't a big deal, get more unpleasant to the west from there. BTW if you stay at Petit Hotel you have access to the pool at L'Esplanade at the other end of Grand Case.
Dave.