I find that titanium exhaust tend to scream a little more than mild steel.
I have a mate that runs a titanium exhaust with no mufflers, it's ridiculously loud and sounds awesome but it drones and has a screamy note to it.
I run a slapped together mix of stainless and mild which has a much deeper note to it. It also doesn't sound like other GTR's. I'm guessing it's because of all the mixed parts on the exhaust.