Trench is a lot noisier, just go to the 109 tram stop at Box Hill for a good experience of the rail noise emanating from Box Hill station a few hundred metres away. Aside from minor patch-up work, the tracks haven't been changed since the station was built 40 years ago so every single set of points has a noisy clickety-clack amplified by all the concrete buildings around it; additionally, the up track through platform 2 is that rough it can be heard in the shopping centre above every time a Flinders Street train arrives, been like that for years.
The only examples of noisy "skyrail" I can think of are the Flinders Street Viaduct and the Swan St bridge, both of which are as old as the hills. On the other hand, Canterbury station is practically silent, the only letdown there is that the tracks are as old as the station so there's some minor rail noise (if anything, some of the noise here is muffled due to having wooden sleepers).
On the subject of rail noise, what happened to the grease pots and/or automatic flange lubricators on the 50 km/h curve out of Ringwood on the Belgrave side? You hear trains screeching around that corner 20 hours a day, the only time it shuts up is when it's raining or there are buses replacing trains. The points at Ringwood are just as worn out as those at Box Hill too, you can hear the trains rumble over them from Heatherdale, and even from Mitcham late at night.