NTP settings seem random - need to lock it down

I have two blueflex speakers and one of the original playbars. The two bluefles speakers are wireless and the Playbar is wired. They have reserved dhcp as well as NTP settings configured with the dhcp scope.

Something that's been bugging me for a while is how often the speakers reach out to the inter for NTP. It's pretty ridiculous. Looking at just the two wireless speakers, they've made 100+ requests for NTP in the last four hours. And they seem to be querying the same SIX ntp servers over and over again, as well as one of the NTP servers I have configured. It's nearly one time request a minute.

23.155.72.147
23.143.196.202
50.218.103.254
23.150.41.123
104.207.148.118

96.245.170.99
172.233.177.198

Is there a reason for this, because it's quite excessive and creates a significant amount of noise on the network. Unless they're losing time synch of more than a few seconds per day, there's no need for all of this traffic. I do see where they are also using one of the NTP servers I have configured, but how do I disable the other six servers? I'm going to have to lock this down at some point and restrict ntp to known good servers, so will this have an affect on the speakers?  

Thanks - logs are attached from my firewall.

edit - ok looks like I can't attach anything. Let me know if it would help and I'll send them.