Do not respond by playing loud noises back, no matter how tempting, that’ll just give him the chance to say “see, they’re the ones doing it”. Going away for a break might be a great idea though, just to get some rest and relax a bit. I’d suggest putting up external cameras covering the whole property, and internals covering doirs and windows first though, just in case he does anything harmful. I know you said he was frail, but you don’t want to take chances.