I have a GKE cluster where all of my nodes get the following events constantly:

LAST SEEN   TYPE      REASON             OBJECT                                                     MESSAGE
29m         Warning   NodeSysctlChange   node/node-pool-5e40a405-u87f
25m         Warning   NodeSysctlChange   node/node-pool-61866872-0sc0
25m         Warning   NodeSysctlChange   node/node-pool-61866872-ozwt
19m         Warning   NodeSysctlChange   node/node-pool-e7c093e6-k2ee

Event details for example:

Name:             node-pool-e7c093e6-k2ee.16ac5739c250cd2b
Namespace:        default
Labels:           <none>
Annotations:      <none>
API Version:      v1
Count:            77
Event Time:       <nil>
First Timestamp:  2021-10-09T10:51:10Z
Involved Object:
  Kind:          Node
  Name:          node-pool-e7c093e6-k2ee
  UID:           node-pool-e7c093e6-k2ee
Kind:            Event
Last Timestamp:  2021-10-28T10:51:10Z
Metadata:
  Creation Timestamp:  2021-10-28T10:51:10Z
  Managed Fields:
    API Version:  v1
    Fields Type:  FieldsV1
    fieldsV1:
      f:count:
      f:firstTimestamp:
      f:involvedObject:
        f:kind:
        f:name:
        f:uid:
      f:lastTimestamp:
      f:reason:
      f:source:
        f:component:
        f:host:
      f:type:
    Manager:          node-problem-detector
    Operation:        Update
    Time:             2021-10-28T10:51:10Z
  Resource Version:   767310
  Self Link:          /api/v1/namespaces/default/events/node-pool-e7c093e6-k2ee.16ac5739c250cd2b
  UID:                db0a837c-1c48-4e91-b576-a52220ece0aa
Reason:               NodeSysctlChange
Reporting Component:
Reporting Instance:
Source:
  Component:  sysctl-monitor
  Host:       node-pool-e7c093e6-k2ee
Type:         Warning
Events:       <none>

I have node-problem-detector installed on this cluster, but I couldn't find any reference to this event in their code/docs.