I have an APC surge protector that is making a loud high pitched noise?

I'm alone at work and no one (naturally) is answering their phone. Here at my workplace we have an APC surge protector that is making a loud constant high pitched noise. It's been going on for over 9 hours said the previous shift before me. I've already looked through forums and no one seems to know what to do about it. I've tried re-powering, but the noise instantly comes back on. Any suggestions? I dont know anything about surge protectors, but it's a big black box that has APC Back-UPS ES 500 Surge Protection written on it. There is a green light that that is blinking on it too. Any help would be appreciated! Thanks!