Playing high bitrate streaming radiostations 24/7 (camper mode, anybody?) would have some effect too, I’d guess.
Depends what is being written to /var. If it is just diagnostics info, probably a lot of that can be turned off if you have access to the OS.
On the machine I'm using right now, (Fedora 32) the top level /var directory looks like this:
ls /var
account cache db ftp kerberos local log nis preserve snap tmp yp
adm crash empty games lib lock mail opt run spool www
Here is /var/log on my machine, a workstation.
dnf is the software package manager on Fedora.
ls /var/log
anaconda dnf.librepo.log-20200607 hawkey.log private
atop dnf.log hawkey.log-20200517 README
audit dnf.log.1 hawkey.log-20200524 samba
blivet-gui dnf.log.2 hawkey.log-20200531 secure
boot.log dnf.log-20190630 hawkey.log-20200607 secure-20200517
boot.log-20200505 dnf.log-20190715 httpd secure-20200524
boot.log-20200506 dnf.log-20190721 java_install.log secure-20200531
boot.log-20200513 dnf.log-20190728 journal secure-20200607
boot.log-20200514 dnf.log.3 kdm.log speech-dispatcher
boot.log-20200521 dnf.log.4 kdm.log-20200110 sphinx
boot.log-20200522 dnf.rpm.log lastlog spooler
boot.log-20200523 dnf.rpm.log.1 libvirt spooler-20200517
btmp dnf.rpm.log.2 maillog spooler-20200524
btmp-20200601 dnf.rpm.log-20190630 maillog-20200517 spooler-20200531
chrony dnf.rpm.log-20190715 maillog-20200524 spooler-20200607
cluster dnf.rpm.log-20190721 maillog-20200531 sssd
cron dnf.rpm.log-20190728 maillog-20200607 swtpm
cron-20200517 dnf.rpm.log.3 mariadb tallylog
cron-20200524 dnf.rpm.log.4 messages wtmp
cron-20200531 dpkg.log messages-20200517 wtmp-20191216
cron-20200607 firebird messages-20200524 Xorg.0.log
cups firewalld messages-20200531 Xorg.0.log.old
dnf.librepo.log fsck_hfs.log messages-20200607 Xorg.9.log
ls /var/log -al
total 81124
drwxr-xr-x. 24 root root 4096 Jun 8 19:15 .
drwxr-xr-x. 22 root root 4096 May 12 23:57 ..
drwxrwxr-x. 2 root root 4096 Oct 21 2016 anaconda
drwxr-xr-x. 2 root root 4096 Jan 28 05:26 atop
drwx------. 2 root root 4096 May 23 13:39 audit
drwxr-xr-x. 2 root root 4096 Apr 21 12:16 blivet-gui
-rw-r--r--. 1 root root 0 May 23 00:01 boot.log
-rw-r--r--. 1 root root 42622 May 5 00:00 boot.log-20200505
-rw-r--r--. 1 root root 23026 May 6 00:00 boot.log-20200506
-rw-r--r--. 1 root root 2861260 May 13 00:00 boot.log-20200513
-rw-r--r--. 1 root root 49867 May 14 00:01 boot.log-20200514
-rw-r--r--. 1 root root 25989 May 21 00:01 boot.log-20200521
-rw-r--r--. 1 root root 423887 May 22 00:01 boot.log-20200522
-rw-r--r--. 1 root root 21431 May 23 00:01 boot.log-20200523
-rw-rw----. 1 root utmp 0 Jun 1 00:01 btmp
-rw-rw----. 1 root utmp 2304 May 25 01:25 btmp-20200601
drwxr-xr-x. 2 chrony chrony 4096 Jan 28 07:04 chrony
drwxr-xr-x. 2 root root 4096 Apr 27 01:30 cluster
-rw-------. 1 root root 13499 Jun 8 23:01 cron
-rw-------. 1 root root 43557 May 16 23:01 cron-20200517
-rw-------. 1 root root 72093 May 23 23:01 cron-20200524
-rw-------. 1 root root 46900 May 30 23:01 cron-20200531
-rw-------. 1 root root 47544 Jun 7 00:01 cron-20200607
drwxr-xr-x. 2 lp sys 4096 May 26 00:00 cups
-rw-------. 1 root root 47216 Jun 8 23:07 dnf.librepo.log
-rw-------. 1 root root 1034305 May 16 23:16 dnf.librepo.log-20200517
-rw-------. 1 root root 369297 May 23 23:01 dnf.librepo.log-20200524
-rw-------. 1 root root 250209 May 30 23:30 dnf.librepo.log-20200531
-rw-------. 1 root root 193744 Jun 6 23:28 dnf.librepo.log-20200607
-rw-r--r--. 1 root root 91030 Jun 8 23:40 dnf.log
-rw-r--r--. 1 root root 1048567 Jun 8 19:15 dnf.log.1
-rw-r--r--. 1 root root 1048503 May 28 14:02 dnf.log.2
-rw-------. 1 root root 698659 Jun 29 2019 dnf.log-20190630
-rw-------. 1 root root 543509 Jul 6 2019 dnf.log-20190715
-rw-------. 1 root root 553595 Jul 20 2019 dnf.log-20190721
-rw-------. 1 root root 531727 Jul 27 2019 dnf.log-20190728
-rw-r--r--. 1 root root 1031163 May 19 17:43 dnf.log.3
-rw-r--r--. 1 root root 832650 May 12 23:57 dnf.log.4
-rw-r--r--. 1 root root 59753 Jun 8 23:07 dnf.rpm.log
-rw-r--r--. 1 root root 1048518 May 22 01:30 dnf.rpm.log.1
-rw-r--r--. 1 root root 1048534 Mar 6 21:47 dnf.rpm.log.2
-rw-------. 1 root root 138896 Jun 29 2019 dnf.rpm.log-20190630
-rw-------. 1 root root 67742 Jul 6 2019 dnf.rpm.log-20190715
-rw-------. 1 root root 92537 Jul 20 2019 dnf.rpm.log-20190721
-rw-------. 1 root root 8910 Jul 27 2019 dnf.rpm.log-20190728
-rw-r--r--. 1 root root 1048549 Nov 15 2019 dnf.rpm.log.3
-rw-------. 1 root root 1048538 Nov 5 2019 dnf.rpm.log.4
-rw-r--r--. 1 root root 0 May 12 23:07 dpkg.log
drwxr-xr-x. 2 root root 4096 Jan 28 11:36 firebird
-rw-r-----. 1 root root 211731 May 4 17:39 firewalld
-rw-r--r--. 1 root root 952 May 4 22:05 fsck_hfs.log
drwx--x--x. 2 root gdm 4096 May 5 13:12 gdm
drwxr-xr-x. 2 root root 4096 May 18 15:30 glusterfs
-rw-------. 1 root root 173601 May 27 2019 grubby
-rw-------. 1 root root 816 Jun 8 21:05 hawkey.log
-rw-------. 1 root root 4692 May 16 21:14 hawkey.log-20200517
-rw-------. 1 root root 6834 May 23 23:01 hawkey.log-20200524
-rw-------. 1 root root 3825 May 30 21:29 hawkey.log-20200531
-rw-------. 1 root root 2958 Jun 6 23:28 hawkey.log-20200607
drwx------. 2 root root 4096 Mar 31 09:20 httpd
-rw-r--r--. 1 root root 0 Nov 23 2016 java_install.log
drwxr-sr-x+ 4 root systemd-journal 4096 Feb 7 2017 journal
-rw-r--r--. 1 root root 0 Jan 10 00:00 kdm.log
-rw-r--r--. 1 root root 2118 Jan 9 17:09 kdm.log-20200110
-rw-rw-r--. 1 root utmp 293168 May 29 18:03 lastlog
drwx------. 3 root root 4096 Mar 24 09:47 libvirt
-rw-------. 1 root root 0 Jun 7 00:01 maillog
-rw-------. 1 root root 0 May 10 00:00 maillog-20200517
-rw-------. 1 root root 0 May 17 00:01 maillog-20200524
-rw-------. 1 root root 0 May 24 00:00 maillog-20200531
-rw-------. 1 root root 0 May 31 00:00 maillog-20200607
drwxr-x---. 2 mysql mysql 4096 Mar 16 07:14 mariadb
-rw-------. 1 root root 1207302 Jun 8 23:40 messages
-rw-------. 1 root root 6778787 May 16 23:50 messages-20200517
-rw-------. 1 root root 31528336 May 24 00:00 messages-20200524
-rw-------. 1 root root 13432656 May 31 00:00 messages-20200531
-rw-------. 1 root root 10680171 Jun 7 00:01 messages-20200607
-rw-r--r--. 1 root root 532 Nov 23 2019 pacman.log
drwx------. 3 root root 4096 Apr 14 11:19 pluto
drwx------. 2 root root 4096 Apr 7 02:57 ppp
drwx------. 2 root root 4096 Dec 17 2018 private
-rw-r--r--. 1 root root 1040 Apr 1 11:23 README
drwx------. 4 root root 4096 May 22 17:06 samba
-rw-------. 1 root root 0 Jun 7 00:01 secure
-rw-------. 1 root root 6319 May 14 16:02 secure-20200517
-rw-------. 1 root root 70683 May 23 13:38 secure-20200524
-rw-------. 1 root root 3239 May 29 22:37 secure-20200531
-rw-------. 1 root root 918 Jun 5 16:15 secure-20200607
drwx------. 2 root root 4096 Feb 25 03:39 speech-dispatcher
drwxr-xr-x. 2 sphinx root 4096 Jan 30 19:43 sphinx
-rw-------. 1 root root 0 Jun 7 00:01 spooler
-rw-------. 1 root root 0 May 10 00:00 spooler-20200517
-rw-------. 1 root root 0 May 17 00:01 spooler-20200524
-rw-------. 1 root root 0 May 24 00:00 spooler-20200531
-rw-------. 1 root root 0 May 31 00:00 spooler-20200607
drwxr-x---. 2 root root 4096 Jun 7 00:01 sssd
drwxr-xr-x. 3 root root 4096 Dec 17 2018 swtpm
-rw-------. 1 root root 0 Dec 20 17:22 tallylog
-rw-rw-r--. 1 root utmp 614784 May 30 02:29 wtmp
-rw-rw-r--. 1 root utmp 1051392 Dec 15 19:29 wtmp-20191216
-rw-r--r--. 1 root root 59406 Jan 9 17:09 Xorg.0.log
-rw-r--r--. 1 root root 64821 Jan 9 16:31 Xorg.0.log.old
-rw-r--r--. 1 root root 47243 Jan 9 13:41 Xorg.9.log
Some people have root access to their MCUs, right ? What does ls /var/log -al look like for them ?