I think I know what you’re talking about and yes I have noticed this before. However, I’m not sure if it’s exactly a ‘volume spike’ since the quality of the laugh seems different before and after the jump. Before the jump it seems a bit garbled, after it sounds a bit better. This may have been a mixing issue. Given I was born many years after Jaws came out and I’ve sadly only caught a showing of it in the theaters a few years ago with the surround mix, I can’t comment on what this instance was in the theatrical release. However this seems to have been a recurring instance in all the video releases including in this clip (skip to 7:06) so who knows?

https://www.youtube.com/watch?v=Gimx8kxykQ8