iced1776 :
Update for anyone interested:
After speaking to Sony again (I had given up for a few weeks) I finally found a tech who was actually willing to research the issue and he has found the same problem before in this model and is 99.9% sure that the problem is a failing processor. The sound drivers aren't actually the issue even though disabling them acts as a quick fix. I sent my laptop out for service today, I'll let you know if the replacement processor does the trick.
Any update on this? After an exhausting endeavour to find a solution to a problem that sounds somewhat similar to what you've experienced - I've tried just about everything from software and driver updates, to CPU load and latency correction, to external USB sound-cards and hardware tests - I've been left without any recourse or respite for my effort. I also have a built-in Realtek sound-card; but an AMD graphics card rather than your Nvidia one.
As with you, my VAIO had flawless audio until about six months after purchase, when I started hearing a 'popping' noise in certain graphically-intensive games. What I found interesting was that if I were to turn off the sound effects but leave background music on, the symptoms seemed to disappear as the game continued. Youtube and music seemed to be unaffected for the most part (a differentiation from your experience), but I also began to notice what I can only describe as the sound I would associate with 'interference' when changing volume or opening an application. The sound exists with or without headphones, and - particularly when opening an application (e.g. music player) or stopping a music video - can be heard in the 2-3 seconds proceeding an event.
I learned to live with these strange anomalies for the most part, but recently the problem has returned to my attention after purchasing an old PC game (a first person shooter : Deus Ex) - a game that should have no problem running considering the specs of the laptop's hardware, and that does indeed run smoothly outside of the aforementioned audio problem. If I stand still, there is no issue and the sound effects of the environment seem to play okay; but once I move the mouse or character, the popping noises become impossible to ignore. Once again, turning off the sound effects while leaving the background music playing removes the issue.
Interestingly, I can hear similar interference to that experienced when opening windows applications (2-3 second delay) during the loading of the operating system, when the windows logo is displayed, and the sound is somewhat reminiscent of that of an amplifier being switched on or headphones being plugged in, but in repeated bursts.
Here is part of my system's dxdiag report (that I picked out somewhat arbitrarily), for anybody else who might have an idea of what this is :
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System Information
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Operating System: Windows 7 Professional 64-bit (6.1, Build 7601) Service Pack 1 (7601.win7sp1_gdr.120503-2030)
Language: English (Regional Setting: English)
System Manufacturer: Sony Corporation
System Model: VPCSB18GG
BIOS: InsydeH2O Version HuronRiver.3.61.05.2051R2087H4
Processor: Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz (4 CPUs), ~2.7GHz
Memory: 4096MB RAM
Available OS Memory: 4012MB RAM
Page File: 2915MB used, 5106MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
DxDiag Version: 6.01.7601.17514 64bit Unicode
------------
DxDiag Notes
------------
Display Tab 1: No problems found.
Sound Tab 1: No problems found.
Input Tab: No problems found.
--------------------
DirectX Debug Levels
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Direct3D: 0/4 (retail)
DirectDraw: 0/4 (retail)
DirectInput: 0/5 (retail)
DirectMusic: 0/5 (retail)
DirectPlay: 0/9 (retail)
DirectSound: 0/5 (retail)
DirectShow: 0/6 (retail)
---------------
Display Devices
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Card name: AMD Radeon(TM) HD 6470M
Manufacturer: ATI Technologies Inc.
Chip type: ATI display adapter (0x6760)
DAC type: Internal DAC(400MHz)
Device Key: Enum\PCI\VEN_1002&DEV_6760&SUBSYS_907B104D&REV_00
Display Memory: 2251 MB
Dedicated Memory: 501 MB
Shared Memory: 1749 MB
Current Mode: 1366 x 768 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: unknown
Monitor Id: SNY05FA
Native Mode: 1366 x 768(p) (59.937Hz)
Output Type: Internal
Driver Name: aticfx64.dll,aticfx64.dll,aticfx64.dll,aticfx32,aticfx32,aticfx32,atiumd64.dll,atidxx64.dll,atidxx64.dll,atiumdag,atidxx32,atidxx32,atiumdva,atiumd6a.cap,atitmm64.dll
Driver File Version: 8.17.0010.1083 (English)
Driver Version: 8.862.4.4000
DDI Version: 11
Driver Model: WDDM 1.1
-------------
Sound Devices
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Description: Speaker/HP (Realtek High Definition Audio)
Default Sound Playback: Yes
Default Voice Playback: Yes
Hardware ID: HDAUDIO\FUNC_01&VEN_10EC&DEV_0275&SUBSYS_104D5000&REV_1000
Manufacturer ID: 1
Product ID: 100
Type: WDM
Driver Name: RTKVHD64.sys
Driver Version: 6.00.0001.6662 (English)
Driver Attributes: Final Retail
WHQL Logo'd: n/a
Date and Size: 6/19/2012 16:54:20, 4065296 bytes
Other Files:
Driver Provider: Realtek Semiconductor Corp.
HW Accel Level: Basic
Cap Flags: 0x0
Min/Max Sample Rate: 0, 0
Static/Strm HW Mix Bufs: 0, 0
Static/Strm HW 3D Bufs: 0, 0
HW Memory: 0
Voice Management: No
EAX(tm) 2.0 Listen/Src: No, No
I3DL2(tm) Listen/Src: No, No
Sensaura(tm) ZoomFX(tm): No
I would greatly appreciate any assistance. Deus Ex is unplayable in my obsessive mind, and storming enemy castles in Total War games is just that little bit less epic when panning across the environment triggers out-of-theme popping sounds. My greatest fear is - as the TS mentioned - that these could be the signs of failing hardware.