IBM NetVista X40 Technical Information Manual page 20

Acoustical noise-emission values
Average sound-pressure levels:
4.6 bels idle
5.0 bels operating
Note:
12
Technical Information
These levels were measured in controlled acoustical environments according
to procedures specified by the American National Standards Institute (ANSI)
S12.10 and ISO 7779, and are reported in accordance with ISO 9296. Actual
sound-pressure levels in your location might exceed the average values stated
because of room reflections and other nearby noise sources. The declared
sound power levels indicate an upper limit, below which a large number of
computers will operate.