Frames per second issue

I looked around a little on the forums and did not see anything related to this besides benchmarks for other games. So let me tell you about my issue, I play World of Warcraft (lets just say a lot) and lately when I have been playing and running around doing dungeons or PvP or even just sitting around in game my fps will drop from the normal amount for my settings to about 2 or 3 fps . The normal fps for my settings is about 80 or 90 if put them on low with nothing enabled I have about 300fps it I put it on ultimate I only run around 40fps. I tried everything I could myself in no particular order reinstall wow, defrag, use no addons, use no sound, use low settings, virus scan, update drivers, and a fresh windows install. My PC specs are as follows:

-Quad Core Processor (Q6600)
-MSI P6N SLI platinum Motherboard
-8GB G.Skill RAM (Model F2-6400CL5D-4GBPQ)
-Nvidia 9600GT 512mb 256-bit Video Card (XFX PVT94PYDF4)
-Western Digital 250GB hard drive
-There is a second hard drive but I can't recall its manufacturer but it only holds music and videos also 250GB
-Pioneer DVD-RW Drive
-I use on-board LAN and on-board sound
-Standard Logitech Keyboard nothing fancy
-Razer Naga gaming mouse

My windows experience rating is a 5.3 determined by my RAM everything else is 5.9 except my Hard drive which is 5.4, I am using Vista 64-bit business.
Some things I have noticed when the fps drop happens:
-Using the tool in the windows sidebar I have noticed my Processor usage jump up to about 90% when this happens it normally sits at about 30-35
-Using task manager and sorting by CPU usage 90% of the time the top user of my CPU is idle followed closely by WoW.exe (world of warcraft) until I lag then a file called audiodg.exe jumps up to about 30-40% processor usage and wow still uses a solid 25-30% during this and all other tasks use up a combined total of about 10%

Any help with this would be amazing, if you need more information I will check back regularly, I just want this to be fixed and blizzard has helped me none.