high cpu on idle state

Sorry to bother if my question is irrelevant
but I really would like to understand why
idle persistent connection would take more than 25% of a cpu

top -c

63844 postgres  20   0 4677440 289168 287320 S  33.9  0.9   0:03.43
postgres: freeswitch freeswitch 10.0.0.1(48634) idle
62774 postgres  20   0 4677480 286488 284636 S  29.9  0.9   1:22.17
postgres: freeswitch freeswitch 10.0.0.228(29664) idle
 4901 postgres  20   0 4677480 280812 278968 S  27.6  0.9   2:43.71
postgres: freeswitch freeswitch 10.0.0.5(39044) idle
 4847 postgres  20   0 4677480 279468 277624 S  24.9  0.8   2:35.25
postgres: freeswitch freeswitch 10.0.0.230(31786) idle

these 4 connections are made through a VPN with tinc.
is this issue a VPN configuration, postgresql or odbc?

Thanks for your help.

David