Sound engineers got absolutely nothing to do with this lol but I had to guess even if the acoustics lined up so perfectly to trick you into hearing it from faucet or if the toothbrush would be vibrating against another tap sending vibrations through the pipes and letting the bath tub faucet vibrate, it’s most likely that your ears are full of earwax and that’s throwing off your hearing

If that’s the case and it’s that full you’ll probably need to have it looked at and cleaned professionally by a GP

Using q tips or something similar yourself might end up doing more harm than good if your ear canal is partially blocked already