Birds go crazy when uncovered

So for as long as I've had my cockatiels I've always put a blanket over their cage at night and took it off during the day but recently during the day when I take it off they just start screeching extremely loud,to the point it hurts my ears and it doesn't matter what I do,they wont stop. Food,water,toys,I try to let them out of the cage but because they're "separated" the male one gets even louder and I feel like just having the cage covered all the time isn't healthy