I have something similar! Well, my opinion on this topic is that there is insufficient bandwidth when it comes to data transfer from the HDD. Now I know it sounds stupid and its just a speculation, but bare with me here. So what I have in my G55 is: SSD plugged into the original SATA3 port of the computer, and the 750GB SSH drive which came with the laptop as I purchased it, I put in the optical drive bay via a caddy. I play a lot of CS:GO and A weak a go I had it installed on my SSD and it ran fine, but what happened is that with time my SSD got full and I had to free some space, so I moved the CS:GO to the HDD in the optical bay. After moving it there and I tried to play the game, the same thing happened to me the video and sound spikes and stutters, like every 10-20 seconds it will freeze for a half a second or so. The stutters are really fast, like the connection between the HDD and the mother board doesn't have that fast transfer for the necessary files to be loaded or something like that. After that frustration I reinstalled the game once again on my SSD and everything worked like a charm. In my opinion this is a hardware problem or some sort of incompatibility. At least that's my take on the topic.

For those of you with stuttering audio problems, try updating the LAN driver (I have a G75VW with the Atheros 8151 chipset). This was the one major cause of stuttering audio for me, regardless of whether the LAN was being used or not. It would also cause spikes that would appear as if the NVIDIA drivers were doing something wrong, but those disappeared after I updated the LAN drivber.

Disabling the LAN adapter would also help, but then I would get issues with various audio software (e.g. Waves plugins) thinking it now was a different computer due to hardware ID changes when disabling the LAN driver.

So, try the latest drivers directly from Qualcomm: http://www.atheros.com/corporate/content.php?nav1=146