High Physical Memory Usage During Full Scan

Over the past few days, my wife's PC has started to act erratically during Full Scans with Norton's 360.  Somewhere between 230K and 300K files scanned, physical memory begins to ramp up gradually from about 15-20% all the way to 96%, at which point Norton's freezes.  It never freezes at the same spot, but usually around 330K files (have no idea how many more files it needs to scan).  The only new program that had been added recently was Malwarebytes, which I have heard mixed opinions about working with (or not working with) Nortons.  We removed it and then ran Norton's Power Sweep (twice), but that did not help.  After several re-attemptes, we eventually did a System Restore and completely uninstalled/reinstalled Nortons.  Then we ran it again....same problem.  The physical memory usage increase does not happen under any other circumstances, only when Nortons attempts a Full Scan.  Quick scans work fine.  Anyone have any thoughts?   Since removing Malwarebytes, we have no other Anti-virus/Anti-Malware etc on the computer aside from Nortons.

Thanks in advance.