Could this be possible? I've burnt some games at 6x, like Fifa 09, and sometimes when I am playing (actually most times), the sound will stop for like half a second, then come back. Gameplay / video etc etc is fine, it's just the sound. The original doesn't have this issue.

I burnt it at 6x which I think may be the issue, instead of 2.4x. I used Verb's, MIS, 2.4x rated to 6x. They cost like $3AUD each DVD so I don't really want to try burning it again @ 2.4x to see if the issue goes.

Is this a common issue when burning at a higher speed? What other issues can arise from burning at higher speeds?

Thanks.

Really depends on your burner, but I know I've had no issues with burning the MIS 2.4 Verbs at 6x on my Pioneer, but this drive is known to be the best drive out there for 360 burning.
Have you tried installing the game(s) in question to your HDD via the NXE menu to see if that alleviates the issue?

Atm I don't have a HDD, but hopefully tomorrow I will! I bought a BEVS WD drive and I'm going to internalize it so I don't have to have a HDD shell, so tomorrow (if it's arrived), I'll be able to copy the game to the HDD and test it.

If copying it to the HDD fixes the issue, what could that mean? DVD drive is to blame? Just a random 1 off bug from the burn?

N.B It's a Pioneer DVDR-216BK, used CloneCD to burn.

If it works, then it could be either the DVD drive is going bad, or somehow those burns were bad.
I would recommend using ImgBurn to write your images instead of CloneCD.
The 216 is a great drive too, so that is unlikely the cause of your issue (I have a 215).

Reason for ImgBurn? Or just preference?

I use CloneDVD2 to copy DVD's so that's why I went with CloneCD over ImgBurn.

Seems to be the app that causes the least amount of issues with 360 images.