A couple of months ago i decided to upgrade my 560ti. I bought a xfx R9 280x(before prices went up), but that died within a month. I returned the 280x and bought a 780(03G-P4-2784-KR), but i am getting these nasty frame drops. At first i thought it was a Windows 8 issue, so i installed Windows 7, but i am having the same problem. Then i thought it might be my power supply(FSP AU-750M). So i put my old Corsair tx750 v1 back in. It seems like my overall fps is higher but when the frames drop it seems to be worse.
If i had to illustrate what is going on it would look something like this

 
I cant say it was happening with the 280x or the 560ti, but it is possible. It happens in any game or even on youtube videos. I dont think it is temperature related. The 780 never goes over 70*c.
I have tried googling this problem but cant find much about it. Im not sure if its a faulty video card or something else, but maybe someone has seen this before.
 
Specs:
Motherboard: Asus p8z77-v pro
Cpu: Intel 2500k(stock speeds)
Memory: Corsair 2x8gb(cmx16gx3m2a1600c11)
Current psu: Corsair TX750 v1
ssd: Intel 530 240gb
HDD: 4x1tb and 1x500gb, 5 in total
Fans: 6x120mm
Sound card: Asus Xonar DG
 
The bios and drivers are all up to date. For some reason i still think its the power supply, but i want to make sure before i spend more money.

Ok, i cant say for sure. but im pretty positive that removed the frame drops i have been seeing.
Thank you. this was driving me nuts.
So how do i figure out which service was causing this?
I am assuming you would need some sort of list.
 
These are the ones that i stopped:
Apple Mobile Device
Bonjour Service
Google Update Service (gupdate)
Google Update Service (gupdatem)
Intel(R) Rapid Storage Technology
Intel(R) Capability Licensing Service Interface
Intel(R) PROSet Monitoring Service
iPod Service
Intel(R) Dynamic Application Loader Host Interface Service
Intel(R) Management and Security Application Local Management Service
NVIDIA Network Service
NVIDIA Streamer Service
NVIDIA Display Driver Service
Steam Client Service
NVIDIA Stereoscopic 3D Driver Service
Intel(R) Management and Security Application User Notification Service

I have that same motherboard its a great MB but can be fussy. But it is  surge sensitive board for sure. As long as your confident about your bios setup, I use a Really big battery backup system. the mother board is sensitive to other electric devisees turning on and off around it. It stopped doing weird things like that once I got the right back up.

Seeing that you do have a sound card, you may want to disable the nvidia hd audio driver in your device manager. Perhaps even try changing the power management mode in the nvidia control panel to maximum.