Bruce can't hear Tony and Jarvis' banter, but he can assume that Tony is in the work area by the volume level of the music that is currently blasting from that general direction. Before acquiring living space with Tony and the other Avengers, he had been used to small quiet places. Here, there is always someone up and about or things exploding or--current situation for example--deafening music. It's a bit overwhelming at times, but he wouldn't trade any of the craziness for his lonely shack in Kolkata.

It hasn't taken him very long to work himself back into the groove of lab activities. Once Tony had gotten him going, it was like.. picking up where he had left off, almost. A different sort of science, perhaps, and a different lab partner. But still familiar and comforting; making it so very easy to lose himself in all of the gadgets and computers. And so, it seems entirely normal to him to come down the stairs and see the Iron Man armor in pieces and to see Tony Stark conversing with the disembodied voice of the AI system.

"Hey, Jarvis. Could you turn the music down a bit? I can hardly hear myself thinking."