Hello -- a single beep occurred every minute or so in a friend's Honda Jazz's most recent journey, different from the seatbelt and key warning sounds. Any ideas?

no year car told or country told.
when it BEEPs use a scan tool to see why with DTC errors
i might be low fuel warning but is just a wild guess.
if one gauge reads wrong I may beep
not MPH
but RPM. , fuel , engine temps too high, or Odometer data is wrong, or corrupted
a door ajar

Sounds like vehicle theft issue. Unhook batt for min and see if it clears...like a reboot. If nada then git it scand at partstr

Check with FIAT service centre but I suspect that it is the immobiliser and alarm arming themselves after the key has been removed and the noise is to let you know that the process is happening

Check the fuses one may be shorting out. Also check wiring to fuse box.

check the drive line "U" joints

check the radio fuse

The audible warnings alert the driver of a system concern or a critical vehicle condition. The radio generates the audible warnings through the left front speaker. The radio receives audible warning requests via the class 2 serial data line from the IPC or body control module (BCM). If the radio receives multiple audible warning requests, the warning with the highest priority sounds first. The following lists the audible warning priority and the pulse rate:
Fast rate chime--200 pulses per minute
Medium rate chime--150 pulses per minute
Slow rate chime--50 pulses per minute
Single chime

Is the sound heard different from typical Audible Warnings ?

Fasten Safety Belt Warning
The radio activates the fasten safety belt audible warning as requested by the IPC. The IPC sends a class 2 message to the radio indicating the chime frequency, slow rate and duration (5 pulses). The fasten safety belt warning sounds and the fasten safety belt indicator illuminates when the following occurs:
• The ignition switch transitions to ON.
• The inflatable restraint sensing and diagnostic module (SDM) detects that the driver's seat belt is not buckled, signal is low. The IPC receives a class 2 message from the SDM indicating the driver's seat belt status.
If the seat belt is buckled when the ignition is turned on, the chime does not sound. If the seat belt is buckled while the chime is sounding, the chime stops. If the seat belt is unbuckled after the initial transition to ON, the chime does not sound.
Headlamps On Warning
The radio activates the headlamps on warning as requested by the body control module (BCM). The BCM sends a class 2 message to the radio indicating the chime frequency, fast rate and duration, continuous. The headlamps on warning sounds when the following occurs:
• The ignition is OFF.
• The BCM determines that the driver's door is open, signal is low.
• The BCM determines that the headlamp switch is in the park or head position.
Key-In-Ignition Warning
The radio activates the key-in-ignition audible warning as requested by the BCM. The BCM sends a class 2 message to the radio indicating the chime frequency, medium rate and duration, continuous. The key-in-ignition warning sounds when the following occurs:
• The ignition switch is OFF.
• The body control module (BCM) determines that the driver's door is open, signal is low.
• The BCM determines that the key-in-ignition switch is closed, signal is low.
Turn Signal Reminder
The radio activates the turn signal warning as requested by the IPC. The IPC sends a class 2 message to the radio indicating the chime frequency, medium rate and duration, continuous. The turn signal warning sounds when the following occurs:
• The ignition switch is in the RUN position.
• The turn signal switch is in either turn position, sensing, within 1 second, an open to B+ transition in the turn signal control circuit, left or right turn.
• The vehicle has traveled a distance of 1.2 km (¾ mi) by counting pulses on the vehicle speed input circuit.
The IPC turns OFF the turn signal reminder when either the ignition switch is turned to the OFF position, or the turn signal switch returns to the OFF position, sensing, within 1 second, no transitions from open to B+ in either of the turn signal control circuits, left turn or right turn.
Additional Chimes
The following chimes will turn ON when an associated indicator/message turns ON in the IPC/DIC:
• ABS indicator
• AWD Disable indicator
• Battery/Charge indicator
• Brake indicator
• Change Engine Oil indicator
• Door Ajar indicator
• Hot Coolant Temp indicator
• Low Brake Fluid indicator
• Low Fuel indicator
• Low Oil Level indicator
• Low Oil Pressure indicator
• Low Tire Pressure indicator/reset
• Low Washer Fluid indicator
• MIL (Service Engine Soon) indicator
• Oil Life Reset
• Park Lamp Out indicator
• Rear Hatch Ajar indicator
• Service Traction System indicator
• Service Vehicle Soon indicator
• TRAC OFF indicator
For a description of an indicator refer to Indicator/Warning Message Description and Operation .
For diagnosis of an indicator refer to Symptoms - Instrument Panel, Gages and Console .

Did the Mechanic check for DTC'S - diagnostic trouble codes in the BCM or insturment cluster ? Did you try a Buick dealer ?

2000 Honda Odyssey the middle seat belt is broken. The seatbelt won't retract. The end of the belt does not come out but the entire seatbelt will come out of the hole.
Any suggestions?

was the vehicle ever in an accident? Does the airbag light come on when starting? If the lamp is burned out it will send an audible beep to warn

As far as the service now indicator, you will have to use an OBDII scanner to clear the service codes out of  your computer in order to turn off the indicator.  Autozone might be able to do this for free.  I know Autozone can read the codes, I am not sure if they can clear them.  I am not sure what the beep is.  Do you wear your seatbelt?  If not buckle the seatbelt and then sit on top of it, if  you absolutely don't want to wear it.  And that should fix it.  If you do wear your seatbelt, the beep might be some sort of airbag warning.