Yeah, that's some serious noise there. There's not a whole lot you can do in this situation. A few of these things might help... or might make it worse... :-)
- Increase 2.4Ghz power to maximum or auto
- Enable aggressive band steering to get clients to move to 5GHz
- Increase roam threshold to 20dB
- Enable off channel scan
- Enable auto RF
- Enable per client rate limits
ALSO, your firmware could use an update... 3.11.3.1 is available.