Hi, is your DS the eldest or youngest? Wondering if his sisters share a room and for whatever reason he feels left out at present.
Does he feel robbed of playtime because it's still light?
Has he recently watched anything scary involving creatures emerging at night? This could have been at home or out of your house round a friend's especially where there are older siblings watching something. The extra noise could be him scaring mosters or ghosts away.
Is he in his last year of Primary School? Could he be aware that his days at his old school are ending and next term he'll start at the bigger school, maybe he is feeling anxious so the bedtime antics are bravado?
Maddening as it is when you want them all off to bed so you can sit down for 5 minutes, maybe you could chat with him, give him a hug. It might feel a bit phoney, but ask him about his day or 3 best things that happened/made everyone laugh.
When my DCs were little they felt reassured if I pottered about in their room or they could hear me cross the landing and into other bedrooms. Doing some chore like folding washing or distributing clean clothes, or whatever; added to which I'd say something like, "Lie down and I'll be along in a minute", then do so. Next time it might be, "I'll be back in two minutes", stick to your word, look in on them. Increase the gaps between dropping in.
Sorry if these ideas are rubbish, just some random thoughts.