Replacement fan ReadyNAS nv+ v2

Appreciate the feedback. I collected some data to show what I am seeing (and hearing), for some reason the temperature and RPM readings of the fan vary over time with a certain interval. What's confusing is that the RPM of the fan falls below the minimum specified of 1350 RPM. But also the fan speed does not seem to react in a timely manner to an increase in temperature.

https://www.dropbox.com/scl/fi/w524uhxynaehefg4nsxt6/log-rpm-fan.png?rlkey=hpb1isx3og5hccr5jhvg6mrci&st=1j7t6fgp&dl=0 

I found the minimum specified RPM specified in /ramfs/enclosure.cfg:

root@vanrun:/# cat /ramfs/enclosure.cfg
fan!!0!!desc=SYS,selfcontrolled=0,minrpm=1350,required=1,alternate=0,path=/proc/fan0_rpm,in_path=/proc/fan0_pwm
fan!!1!!desc=,selfcontrolled=0,minrpm=0,required=0,alternate=1,path=,in_path=
fan!!2!!desc=,selfcontrolled=0,minrpm=0,required=0,alternate=2,path=,in_path=
fan!!3!!desc=,selfcontrolled=0,minrpm=0,required=0,alternate=3,path=,in_path=
fan!!4!!desc=,selfcontrolled=0,minrpm=0,required=0,alternate=4,path=,in_path=
temp!!0!!desc=,mintemp=0,maxtemp=80,divider=1000,path=
temp!!1!!desc=,mintemp=0,maxtemp=65,divider=1000,path=
temp!!2!!desc=,mintemp=0,maxtemp=0,divider=1000,path=
vol!!0!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!1!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!2!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!3!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!4!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!5!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!6!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!7!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!8!!desc=,minvol=0,maxvol=0,divider=1000,path=
vol!!9!!desc=,minvol=0,maxvol=0,divider=1000,path=

Which gets loaded at boot I believe from the database /frontview/conf/enclosure.db:

root@vanrun:/# sqlite3 /frontview/conf/enclosure.db
SQLite version 3.7.3
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> .schema sensors
CREATE TABLE sensors ( id integer primary key autoincrement, model text, pcbid integer, board_rev integer, system_rev integer, vpd_ver integer default 0, vpd text, paths text);

sqlite> select * from sensors order by rowid desc LIMIT 1;
20|ReadyNAS NV+ v2|-1|-1|-1|1|
minrpm: 1350
minpwm: 165
maxtemp0: 80
mintemp0: 0
maxtemp1: 65
mintemp1: 0
maxtemp2: 0
mintemp2: 0
cpu_target: 0
cpu_tolerance: 0
labelfan0: SYS
reqfan0: 1
selffan0: 0
altfan0: 0
minfan0: 1350
typefan0: 1500
|faninput0: /proc/fan0_pwm
fanpath0: /proc/fan0_rpm

sqlite> select vpd from sensors where id=20;

minrpm: 1350
minpwm: 165
maxtemp0: 80
mintemp0: 0
maxtemp1: 65
mintemp1: 0
maxtemp2: 0
mintemp2: 0
cpu_target: 0
cpu_tolerance: 0
labelfan0: SYS
reqfan0: 1
selffan0: 0
altfan0: 0
minfan0: 1350
typefan0: 1500