Olivier's apartment is well located in Paris. Around a 15 minute walk from Gare Du Nord and also the same in the other direction down to the Pompidou Center.
Olivier met us on arrival, he gave us a good tour of the apartment explaining how everything worked. He also gave us a great recommendation for a local restaurant. We were staying only for one night, but he had a long list of other places to try if you are there longer.
The building itself was quiet, there was a little bit of street noise when we were going to bed, but it didn't last too long and didn't stop us sleeping. Nothing more than you wold expect in a busy city. We didn't hear or see any neighbours.
I would definitely use Olivier's apartment again in future.