Check the page file. In the control panel>system
go to the advanced tab then click the setting button of performance, then advanced. This varies depending on the amount of ram but it usually is quite large. Considering the differences are all about a gigabyte I would suggest this as the reason plus the removal & addition of files. Try changing it to 1mb and see if it stops. If it does return it to about 2times what ram you have and there is the answer.