Since it just started, it is most likley a loose or poorly connected wire (corrosion). Or, something broke inside the amp or speaker.
If you are sure of all of the connections, and the rear speakers do not have static, then try reversing the front and rear speaker leads at the amp.
Now, if the front continues to buzz, and the rear does not, then your problem is in the front speaker lead, or in the front speaker itself.
Now, if the rear speaker starts to buzz and the front is fine, you probably have a defective amp.
I would try one wire at a time, not a whole re-wire, that could be a lot of work and you still might have the same problem.