I have to parakeets and they have always done well together, except at night my female(Jerry) starts to bite and make some sort of growling noise at my male(falco) as soon as I cover the cage with a blanket. This started happening a couple of months ago. Any Ideas to make her stop besides spliting them up?

Your cage may not have enough space for the 2 budgies & this could be causing the problem.

Apart from separating them perhaps if your cage isn't very big you could get a larger one. They do need a lot of space between them so when their are times one is cranky or too close, the other can easily escape to it's own space.