My phone won't stop uploading. No idea what.

My phone won't stop uploading. It basically uploads at its maximum bandwidth for almost all hours of the day.. According to My Data Manager it's caused by Google Contacts Sync, which has uploaded almost 700mb in the last 4 or 5 hours. I've gone into my accounts settings and turned contacts syncing off, but it's still uploading, which has me concerned.

As you can imagine, this is destroying my battery. Restarting has no effect. I could factory reset, but I'd rather figure out what's causing the problem. Bad app update? Haven't installed anything out with the Play Store other than a couple of Humble Bundle games, and they were long before this started happening.