Budgie incessantly chirping at night

Hello there! I’m new to this forum, and I’m in search of some help regarding one of my budgies. I have two at the moment - Sky, who is several years old, and Ash, who is about six months old. Sky has recently developed a very annoying habit of chirping incessantly at nighttime, and I mean a repetitive call that she can do for hours. They do sleep in my bedroom (it’s the only suitable place in my home for them) but even with silence, lights out and a blanket over the top she will not stop chirping. Not only is it quite frustrating to accommodate my life around her, Ash is clearly getting little sleep and I fear he may seriously be affected if this becomes long term. Does anyone have any ideas why she won’t stop chirping? She continues with or without attention, and she always acts erratic at bedtime which is even more stressful. Any tips are much appreciated.