Performance related lag spikes

Hello Everybody!

I am a new member to this forum, so please bear with me here.

Recently I have been getting random lag spikes, where my computer would freeze for a duration of about 2 seconds and would happen every 20 seconds or so. This becomes really frustrating when I play games or even just go about my daily activities, as you can imagine.
The weird thing is sometimes a lag spike occurs... I keep hearing a usb device connecting (the default sound that windows makes when a usb device connects or disconnects) through my speakers. I only have three devices plugged in to my computer via USB: my mouse, keyboard, wireless network card.

I have tried every trick in the book (at least that I know of), such as:
-virus scans (using AVG)
-malware scans (using Malware Bytes)
-registry fixes/disk cleanups (using AML)
-system restore
-disk defrag
-driver updates (video card, network card, etc.)
etc...

My system specs:
AMD Phenom 9850 @ 2.5Ghz
ATI Radeon HD4870 @ 512MB GDDR5
OCZ Platinum Series RAM @ 4GB Dual-Channel
Seagate Barracuda 500GB HDD @ 7200rpm
Thermaltake 750W power supply
Windows 7 Ultimate 64-Bit

I am running out of options, and the last thing that I want to do is re-format my hard drive! Any help would be much appreciated!
Thanks :)

Did this recent problem co-incide with the use of AML? {registry fixes/disk cleanups}

1. I note they say

AML Free Registry Cleaner offers a level of registry cleaning and penetration much deeper than that. AML Free Registry Cleaner is particularly good at identifying and correcting multiple entries in your Windows Registry...

2.If necessary you could revert.

AML Free Registry Cleaner also makes a backup before making any drastic changes so that if the worst does happen, you can always roll back although if you do break your OS badly, this could prove difficult.

Reference >AML Free Registry Cleaner


FYI.
Current accepted wisdom with Win 7 is to NOT use a cleaner.

If you ever think your Registry needs to be cleaned, repaired, boosted, tuned-up, cured, tweaked, fixed, or optimized it shouldn't.

In other words, injudicious use of "Registry cleaners" CAN cause problems.

Thanks for responding guys!

@JMH
Sadly, that backup option is user triggered, and I have not created a backup option whenever I did the "registry fixes", I know, mistake on my part .

@whs
I don't see anything alarming in device manager. What should I be looking for when you say "yellow flag"?

Please anybody else, feel free to throw something at me, I really need to fix this problem!
Thanks!

I just installed a brand new copy of windows 7 (without reformatting), and I have gone ahead and deleted the windows.old folder using disk cleanup utility. I am still getting the same problem, random lag spikes, and usb sound comes up once in a while. Any suggestions from this point?