Just a general suggestion, does the audio switch when there isnt a game running, like does something pop up saying "an audio jack has just been plugged it/unplugged" mine does that, and it required me having to go into my sound driver and disable the front audio port detection, fixed it up nicely
Uhm, about the lag, try disabling all sound via going into control panel, finding sounds, and disabling everything on that list (should just be your speakers)
its a longshot but maybe? it will help us diagnose also
if nothing else try uninstalling your sound drivers and reinstalling them?
I don't think its a audio issue since when lag spikes happen usually the pc has to catch up with all its calculations so it stops sound, etc...
Did you remember to plug the power cord into the card? also is the fan on the card spinning, if not take it back, post your temperatures here after downloading + installing HWmonitor then Prime95 (just download no need to install) and furmark
now what I want you to do is reboot pc after installing those things, open HWmonitor, let it sit for about 5-10 minutes, open prime 95 with HWmonitor still running and start prime 95, let that run on stock settings (just hit go). keep it running for about 15-20 minutes, after that you can stop it, HWmonitor will mention temps, write them down and post them here, just the CPUtin and the CORE # temps, minimum and maximum. (note you can stop the test by going into option and hit stop test) (ALSO NOTE, DONT DO ANYTHING WHILE RUNNING THESE TESTS, nothing bad will happen it just tends to make them less accurate)
After you have all that done run FUrmark while HWmonitor is open (note starting temps of GPU, write it down) let that run for 15-20 minutes then report back here with max GPU temperatures
(NOTE DONT DO THIS TEST IF YOUR GPU FAN DOESNT WORK, cuz your probably gonna break it... since... they... kinda need to uhm... spin...)
Sorry for the bad grammar, I got lazy.