Thanks, but not seeing any other broadcast traffic being duplicated or similar. The Meraki's are on their own PoE switch, and if I disable the uplink port to our main switch the traffic instantly drops from 5MB/s to nothing (of course), but as soon as I enable the port again it goes mental.
Additionally, if I run the packet capture on the Meraki dashboard, selecting the AP's, this also shows the Meraki sending all of the LLDP broadcasts, so this is definitely coming from the AP itself.