Hello. I got the same problem on my nexus 4. It`s used over 9GB over 2-3 days. problem began when i flashed on my nexus latest pa gapps.
Maybe that is the problem ?. I used my actual ROM before, and it wasn`t using so much transfer. My actual gapps is called pa_gapps-stock-4.4.2-20140123-signed.zip and i think they causes the problem.
I did factory reset and install everything as before but i used pa_gapps-stock-4.4.2-20131215-signed.zip.
Everything is ok now so i`m sure problem is in latest pa gapps.
Can anybody tell me what Google keyboard transfers over WiFi???
It`s one of the many Google bugs, i don`t know what it download all time, but do what i said an everything will be all right.