Pihole running nicely, some unexplained name lookups

I have several other pi servers on the same network as the pihole. one of these is a slightly venerable beast, due for a rebuild soon.
However its doing something strange …

netadmin@watchpi ~ $ cat /etc/os-release 
PRETTY_NAME="Raspbian GNU/Linux 8 (jessie)"
NAME="Raspbian GNU/Linux"
VERSION_ID="8"
VERSION="8 (jessie)"
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"
netadmin@watchpi ~ $
eth0      Link encap:Ethernet  HWaddr b8:27:eb:3e:6a:ab  
          inet addr:172.25.25.149  Bcast:172.25.25.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:160602 errors:0 dropped:0 overruns:0 frame:0
          TX packets:91756 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:123372072 (117.6 MiB)  TX bytes:22781986 (21.7 MiB)

eth1      Link encap:Ethernet  HWaddr 00:0e:c6:81:79:01  
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:4909323 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:45409508 (43.3 MiB)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:1109 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1109 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:93873 (91.6 KiB)  TX bytes:93873 (91.6 KiB)

It’s spitting out a pair of name lockups every five minutes for;
ping.local.shoka.net

|2020-01-07 15:55:08|A|ping.local.shoka.net|172.25.25.149|OK (cached)|    NXDOMAIN (0.3ms)| Blacklist|
|---|---|---|---|---|---|---|
|2020-01-07 15:55:08|A|ping.local.shoka.net|172.25.25.149|OK (forwarded)|NXDOMAIN (1.7ms)| Blacklist|
|2020-01-07 15:50:08|A|ping.local.shoka.net|172.25.25.149|OK (cached) |NXDOMAIN (0.3ms)| Blacklist|
|2020-01-07 15:50:08|A|ping.local.shoka.net|172.25.25.149|OK (cached) |NXDOMAIN (0.3ms)| Blacklist|
|2020-01-07 15:45:08|A|ping.local.shoka.net|172.25.25.149|OK (cached) |NXDOMAIN (0.3ms)| Blacklist|
|2020-01-07 15:45:08|A|ping.local.shoka.net|172.25.25.149|OK (cached) |NXDOMAIN (0.3ms)| Blacklist|
|2020-01-07 15:40:08|A|ping.local.shoka.net|172.25.25.149|OK (cached)|    NXDOMAIN (0.3ms)| Blacklist|
|2020-01-07 15:40:08|A|ping.local.shoka.net|172.25.25.149|OK (cached) |NXDOMAIN (0.3ms)| Blacklist|
|2020-01-07 15:35:08|A|ping.local.shoka.net|172.25.25.149|OK (cached)|    NXDOMAIN (0.3ms)| Blacklist|
|2020-01-07 15:35:08|A|ping.local.shoka.net|172.25.25.149|OK (cached)|    NXDOMAIN (0.2ms)| Blacklist|

Anybody seen this before, any suggestions why its doing it?
Harry