So when I shift into sport mode in my 2010 GT Speed W12 I can't really notice the difference in sound.

Having stated this when I recently drove a 2013 GT Speed W12 the sound was night and day different when I put it in sport mode.

Is this normal?

 

You should notice the difference.
Check your exhaust flap actuators, they may be seized.
A good dose of WD40 and manually manipulate them a few times should sort it.
It's unlikely to be the vacuum pipes as the vacuum keeps them closed.

 

Before I modified my 07 GTC I never really noticed a huge difference in the sound on sport mode. I always thought the car sounded a bit soft for a big displacement sporty car.

 

Aside from faulty actuators (which may still be your problem) I remember test driving a 2011 Speed around 2 years ago and I do not recall noticing any significant change in the sound. Even in my 2011 Supersports the sound was pretty much the same with or without the Sport mode when the engine was idle and the car was still. When accelerating it was a lot louder though - a deeper sound. However, in my 2014 Speed it is night and day. Not only it is audibly louder than my Supersports (and that's inside the car) under acceleration, but even at idle on top of sounding louder, it also has a cool sound similar to a mild cam lope. Very cool.

That being said, if you want to hear what sex on wheels sounds like, test drive a 2014/2015 V8 S in Sport mode. Somehow they made it sound like a naturally aspirated muscle car exhaust.

 

thank you.

I agree about the later model being night and day. Also v8S is just so nice and I can't wait to buy one.