on my old HP Pavilion 7840 PC (intel pentium celeron 766mhz with 384mb of RAM, Intel 810 graphics controller, Crystal WDM Audio), FCEUX runs okay with no crackling sounds if I lower the Sound Rate from 44khz (44100 Hz) to 22khz (22050 Hz). lowering the video resolution from 1024x768 to 800x600 did nothing to help with the sound, that I know for sure.
on my other PC [custom made; 1Ghz Pentium 3, 512Mb of RAM, VIA Tech VT8361 graphics controller, SB (SoundBlaster) PCI WDM driver, WinXP SP3 Home], I haven't had much luck resolving some of the sound problems with FCEUX.
just wondering, buddwm, do all your three computers use Win7? I use WinXP SP3 home edition on both of my computers.
you could try changing the "latency" of your sound and video cards by using
PCI Latency Tool. I use PCI Latency Tool v3.0b3 to make some changes with the latency on my custom made PC. OR you can try to adjust the sound latency from FCEUX and play around with the other sound options.
btw, I'm using FCEUX SVN 2043. Find the latest FCEUX SVN build at Emucr.com.