my denso alternator failed on vectra c and i replaced with an rtx one with a modified pulley design,

anyway after 3 weeks that failed so i swapped it under warranty, after about 8 months ive just recently been hearing clicking/clacking noises and i can see the lights dimming, it only happens if i dip the clutch pedal and the revs go down to idle (only when I drop the clutch or the revs go down to idle), once it happened before i revved the hell out of it and it sorted it, tonight it started it again and seems to have stopped after i revved it a few times,

i shone a line as i reved it and let the revs drop to idle and I could see for a split second the alternator shuddering if that makes any sense with a slight affect on the engine (like a misfire but not a misfire, as if the pulley is holding back the engine if that makes sense via the aux drive belt)

is this a failing one way clutch on the pulley of the alternator?