All driven by price, when all the monkeys sell cut price there's nothing to attract or keep good people, the industry has been driven into the floor by the tit's in it for a quick profit and selfish gain.
Remove the wiring from the cct and replace with a link, if it cures it then it's the PIR or wiring. Also worth replacing the battery if it's over 4 years old.
Then short the wiring at the PIR if that cures it then look at replacing the PIR.
I always used to wrap insulating tape round my ceiling fitters wire etc, used to cringe @ live mains in ceilings / voids etc.
eta, that **** also reminds me of the coil in a tape measure, like a wild rattles with a razor body.
Having said that I suppose your OK JW?