This is typical of the type of thing you'd see in an emergency ballast here.
(in this case it has 'D' batteries, others have 'C')

These units are not meant to be taken apart & repaired/batteries replaced/etc ... but that doesn't mean they can't be taken apart

This particular one late last year started buzzing (kinda like a loud annoying magnetic ballast), so I simply unplugged the fitting/disconnected the battery.
When testing one night I also discovered that the lamp flickers dimly when its plugged in (and mains ballast turned off...I'd be afraid of what might happen if the mains ballast was on )

I don't know what's wrong with it, bad relay maybe? (I know the battery is bad too but it buzzes even with that disconnected) And Capacitor C4 is slightly buldged on top, so maybe its on its way out as well.
Probably isn't even worth the cost to repair, even if I can figure out the issue.

Looks like the battery is completely replaceable 6V 5 cell D the buzzing does sound like bad relay! I've had a few do that here

The relay will be buzzing because it's trying to close but the coil isn't getting enough power to do so. Looking at that bulging capacitor, it appears to be right after a bridge rectifier so will be the DC smoothing capacitor. Looking up the relay part numbers, it appears they have 5vdc coils so said rectifier & capacitor will likely be supplying the relays. Could be worth changing that capacitor, probably only a few cents from eBay?

Interesting worth a shot!

I agree, the capacitor will be the problem

Might just have to try replacing that capacitor then simple enough to do.

@Kev:
Yep that battery pack could easily be replaced...even though it says right on the top of the thing: "battery is not replaceable" "replace entire unit when necessary"

Seems a bit of a waste to bin the whole ballast. Over here the batteries are external and can be replaced easily every few years.