We have a Gold Capped Conure and we love her to bits! she CAN be loud, however she rarely is. If the neighbourhood Red Tailed Hawks decide to fly about she cranks it up to full volume, but otherwise only when she's excited, such as when she wants to join in on the conversation
Usually she makes quiet vocalizations. Their voice is as loud as a sun conure but the difference I have noted is the frequency of vocalization is what sets them apart and that rings true for our household, ours is very quiet.
The minute a hint of cage aggression crops up, just rearrange the cage a bit and poof! it's gone. I was told 5/8" bar spacing was appropriate for a Gold Capped and this was the cage we got. At the time it was the biggest we could find with the right bar spacing. If you find a bigger cage let me know.
A&E Cage Co. Large Play Top Bird Cage & Reviews | Wayfair