When exactly do you notice this noise? I have heard something similar when accelerating hard after not accelerating hard.....understand; like getting on it about 75% throttle as opposed to 45% in 4th or 5th gear. From what I can hear it sounded like rubbing plastic, didn't sound like a mount.
Im not too worried about it because I have not heard the noise in quite a while but It would be good to have someone diagnose the issue.