I am using Sp2013 Standard server, with 1 APP, 1 WFE, 1 Workflow and 1 Clustered SQL. Everything was all great until Monday Morning (7-28-14). Thats when Event Log started to fire off following messages:

Log Name: Application Source: Microsoft-SharePoint Products-SharePoint Foundation Date: 7/28/2014 1:30:12 PM Event ID: 5586 Task Category: 
Database Level: Error Keywords:
User: Domain\svc_sp13_frm Computer: computer name Description:Unknown SQL Exception 18452 occurred. Additional error information from SQL Server is included below.
Login failed. The login is from an untrusted domain and cannot be used with Windows authentication. Event Xml: 5586 15 2 3 0 0x4000000000000000 131333 Application computer Name 18452 Login failed. The login is from an untrusted domain and cannot be used with Windows authentication. 

I checked SQl Log at the Same time this is what i found:

07/28/2014 13:30:12,Logon,Unknown,Login failed. 
The login is from an untrusted domain and cannot be used with Windows authentication.
 [CLIENT: ] 
07/28/2014 13:30:12,Logon,Unknown,Error: 18452 Severity: 14 State: 1.
 07/28/2014 13:30:12,Logon,Unknown,SSPI handshake failed with error code 0x80090311 state 14 while establishing a connection with integrated security; 
the connection has been closed. Reason: AcceptSecurityContext failed. 
The Windows error code indicates the cause of failure.
 No authority could be contacted for authentication.
 [CLIENT: ] 07/28/2014 13:30:12,Logon,Unknown,Error: 17806 Severity: 20 State: 14
 

All of my Sites and Services are working as expected, but i am confused why did sharepoint started to fire off such errors.

Servers havent been rebooted or has been made any changes recently for both Sharepoint and SQl.

Thank You