Reporting Services and SharePoint warnings in ULS logs

We have running SharePoint 2010 and using SQL 2008 R2 reporting services. 

Everything works fine for a month and for some reason reports stop rendering in SharePoint. To fix the issue we go to SharePoint Application server and restart SQL Server Reporting Services (MSSQLSERVER) and everything starts to work. Checking the ULS logs we find the following warning:

06/05/2013 07:36:20.48ReportingServicesService.exe (0x5364)                 0x4BC8 SharePoint Foundation                 General                                       8m90     Medium              135 heaps created, above warning threshold of 128. Check for excessive SPWeb or SPSite usage

We checked the Reporting Services logs and could not find any relevant information that points to the root cause of the issue.

Any ideas what might cause this issue? I need to further troubleshoot the issue, but don't know what else I need to do.

Thanks,

Yassar