I run a modest DAW setup, on a Toshiba Satellite L510 [2.3 GHz Dual Core, 1 Gig RAM]. The onboard sound output [High Definition Audio] was ok, and the mic input was horrible [noise floor 65-55 dB!], as is typical with laptops, mostly. Since I use an entirely virtual studio mode of production, and I only input vocals for demos ... I bought a Creative SB Play [USB soundcard thumb-drive], as that's the best I can get here; [my locale here have never heard of M-Audio or Behringers!].
Funny enough, the noise floor is even higher now [41 dB], though the recording is now a slightly improved mess! [Soundforge's spectrum analyser shows me a large DC offset].
I have researched all forums. The best and only solutions by smart folks out there were (i) run on batteries, since the AC power is the cause, OR (ii) cutoff the ground on the AC power plug, or use a "3 pin-to-2 pin" multiplug/ adapter.
Sadly, for me ... NEITHER worked. My audio/ mic input meter shows that constant (and sometimes "lashing"] noise floor at 41 dB [even with my mic boost off, and mic level as low as 10% in the windows mixer].
I read one article by someone who was knowledgeable on electronics, saying something about adding capacitance across (?) the "floating" audio jacks on laptops. Now, I'm not that knowledgeable on laptop/ electronic circuitry ... and all I know is that there is large DC interference on my USB AS WELL!
Please help me figure out and fix this somehow. [My current location offers no expertise on such matters.] I really appreciate the help. Regards.