If to go by what Star Wars depicted it must be pretty loud
On more serious note it is a good question. I would imagine it will vary model to model as laser or not probably some cooling will be required when high powered electronics are at play.
@mb3195 could probably let us know about the difference of his Sony Vs x7900
The Sony is slightly quieter than my 7900. The fan noise is more consistent so becomes less noticeable. I also run my laser in 100% output all of the time, whereas I had my 7900 on low lamp most of the time. If I drop the laser to 80% it becomes almost silent, but the noise at 100% isn’t loud enough for me to worry about.