Sorry for disturbing but my laptop has come up with another problem.
The left speaker gives off a screeching noise very often while playing sound, be it games or movies.
Most probably a hardware problem, but not exactly sure.
I'm no techxpert, much less an electrician or have much work experience thus, but I've found that feedback loops (caused by output from your speakers or receiver getting 'back into' another port, like the Line-In or Microphone jack) sometimes just by the magnetic fields a speaker puts out depending on how cranked up the volume is and, importantly, how close the speaker and coils are to your soundboard/computer) are often the cause of what you're describing, at least on a basic level. If there are no other faults in your JBLs (they're on the high end of speaker/audio manufacturers as I know them) and the screech in one speaker is the only weirdness that's happening, if it's at all possible move your speakers a fair ways from your computer and- importantly- any sound input jacks feeding into your laptop, even the sound card ports as a whole- and try cranking up the volume or bass with the same setup sound-wise (other than your receiver and/or speakers moved away from your rig) and see if that helps at all.
A lot of speakers aren't built with magnetic shielding involved, which of course can affect a computer in more ways than audio troubles, but assuming your JBLs aren't shielded (or are cranked up high enough that it'd trip a feedloop anyway) and you've got them on both sides of your laptop when you listen to your music with the sound up, that's an entirely possible source for your troubles. If you've got a stereo-to-mono cable (with the point in mind that it seemed to be only affecting the one speaker in your description) try 'shutting off' one of the stereo channels, either the one being affected with the 'squeal' or the other. In fact, now that I think of it, you can probably isolate one channel or the other in your Sound Manager (I assume it might be RealTek, but I know you can get some really high-end soundboards and if you've got a pair of JBL outputs you might very well have something a lot more sophisticated than I'm used to ^_^), which may go under a different name in Windows 7 than XP 64-Bit but I imagine you know what I'm referring to.
I hope this is of some help to you; I use my computer for most of my digital music playback and definitely all of my video watching & gaming, and I know how much I count on mine. My setup's pretty basic as digital sound output goes; I have a 0.5mm-to-RCA (one end like a standard headphone jack, going into my motherboard's back output jack, and the other end into the Aux RCA port of my old 400W NEC analog receiver, with two 200W Technics tower speakers from Circuit City several years ago for my birthday, which pump the moosik like a dream) cable that feeds into my receiver. Nothing ubercomplex, and my new rig (arriving on Friday, and whose specs are described in my 'My Computer's Specs') will use the same setup, cables and all. ^_^
-Worker.
