All Audio and Video Stuttering/Glitching/Grinding in Slow Motion on All Players

This was originally posted at Tom's Hardware with pretty laughably poor results. I'm sorry, MG, I'll never stray again, honest:

ThinkPad W520 4282-4YU
Core i7-2860QM @ 2.5GHz
12GB RAM
NVIDIA Quadro 2000M
Win 7 64-bit SP1

Purchased pre-owned, has been absolutely nothing but trouble from the beginning. First attempts to reformat did not take. Determined 500GB HDD was busted. Replaced with 120GB SSD from another ThinkPad. Expected a machine with these specs to purr with multiple tab browsing, hi def video playback, Photoshop CS6 & Lightroom, gaming, win explorer navigation and general multitasking. Instead it putts, sputters, and spits out about 6 BSODs per day, most of them blaming Peer Guardian and ntoskrnl.exe. PG was removed weeks ago, and the screens are about 25% less frequent. Unlocker also causes instant crashing. Browsing is slow, file and folder navigation is slow, assigning higher process priority in task manager does not help, neither does turning off seemingly unnecessary services. A good 50% of Lenovo's bundled and built-in utilities and doo dads have randomly stopped working (battery meter doesn't show remaining %, no more access manager, hotkeys/fn keys and volume adjustment buttons intermittently stop working). The list goes on and on.

The latest and greatest grievance, and the one I'd like fixed with the TH community's gracious help, is the following:

All audio and video sporadically lag, glitch and sputter in sync with what appears to be fluctuations in CPU usage, though even with all non-Microsoft services turned off and all programs closed, the problems persist, if only to a lesser degree. Video and audio in browsers, offline media played from one or more drives, possibly even windows sounds are all subject to this equally. Sometimes it has the appearance of the video and audio kind of grinding in slow motion, other times the audio grinds while the video plays at normal speed, desyncing the two until a random hiccup quickly fast-forwards the audio up to the current frame, often there's just audio clicks and burps.

HD Tune tells me my 1TB UltraBay drive and internal SDD are in perfect health. MemDiag comes up clean as well, as does a ClamWin scan (Malwarebytes & Spybot S&D pending). This machine has stumped me to the point of throwing it on Craigslist as an 'As-is' for 50% of the price I paid for it. I may hang onto it and reformat with linux, but my hopes aren't high. I will be the first to admit my ignorance of some user error causing all or most of these problems, but I've tried everything I know how to and nothing's worked.

Willing and able to provide any additional info upon request, and/or run any additional diagnostics/scans.

Any and all help greatly appreciated.

-Danny