PC slow down due to unknown Antivirs activity with great impact on hdd disk performance

Hello,

We are using Symantec Endpoint Protection version 12.1.3001.165 - English and Symantec Endpoint Protection version 12.1.2015.2015 - English

Affected OS: Windows 7 and Windows 8, 32 and 64 bit

Problem is that several times per day on may PCs disk queue is reaching 5-10. PC starts to work very slowly. Windows performace monitor shows, that a lot of files are accessed and read simultaneously by system process. After Antivirus deletion everything starts to work good. This activity is not displayed in any logs files on SEP client or SEP management server.

This started after Antivirus upgrade from 11 to 12 version. Please help me to resolve this issue

Thank you in advance

Dima Reznikov