Horrible Performance Seagate 7200.12

A few months ago, I built a desktop and used two Seagate Barracuda 7200.12 1TB HDDs as my storage devices. For a while, the machine was blazing fast for everything I was doing (surfing, photo editing, data backups). For background purposes, I am running the following:

OS: Windows 7 beta

CPU: Intel i7 920

RAM: 6 GB Corsair XMS3 DDR3 SDRAM

MOBO: ASUS P6T SE LGA 1366 Intel X58 ATX Intel Motherboard

Video Card: MSI R4670-2D512/D3 Radeon HD 4670 512MB 128-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card

PS: OCZ ModXStream Pro OCZ700MXSP 700W ATX12V V2.2 / EPS12V SLI Certified CrossFire Ready 80 PLUS Certified Modular Active PFC

2-3 weeks ago, I started noticing that typing and mouse performance was suffering. I would type and letters wouldn't show up after several were typed (For instance, I tried to type "jkjkjkjkjk" and I would get "jkjkjkjjjk" ) Sometimes the mouse clicks were not registering to the point where I had to double or triple click for single click actions.

I initially thought my virus scanner (AVG at the time) was the culprit and was creating some process that was hanging the system. I didn't see any signs of this in the Task Manager. I uninstalled it but the problem still continued.

After some more online searching, I downloaded HDTune to see what was going on. I was not hearing any horrible noises from my HDD so I didn't think it was failing. A check for disk errors in HDTune also revealed no issues. However, the performance chart revealed a significant performance drop in the transfer rate. It initially starts out in the ~120 mb/sec range and then drops precipitously. Here's the graph:



Notice the huge drops every so often with the largest one occurring around 58%? I have no idea why that is happening.

Here's a screenshot of the Task Manager if it helps:


I posted in this forum because I'm not quite sure where to start at this point. Here is some other information that may help diagnose the problem.

-The slow typing issue occurs even during username and password entry for Win7. I thought it might be Win7 but the problem occurs when I type my username and password for Ubuntu as well. (My machine has dual boot for Win 7 and Ubuntu using Grub).

-Sometimes the problem is so bad that I can't type at all. I hit the keyboard and nothing changes on-screen

I've tried some Google searching but haven't had any luck finding anything. I appreciate any help people can give me here.

Run antispyware, trojan and antivirus software.