The jet fan is contained and has a more restricted cone of noise.
I've heard from a few sources that one reason modern airliners are quieter is because their engines have a high bypass ratio. The blanket of ambient air that is bypassed shields the exhaust gasses that exit the combustion chamber. Its this blanket of bypassed air that also reduces or blocks the noise, as most of the roar is from the exhaust gases.
The Tornado GR4 RB199 engines have a low bypass ratio therefore sound like variable noise, constant air speed.