Without knowing more details on the account setup, we can provide some potentials that can be checked:
1. Verify if the extension making the outbound call is part of the automatic call recording feature. If so, check to see if the "Play periodic tones for outbound calls" is enabled for the automatic call recording feature. You can check this under the Phone System / Auto-Receptionist / Call Recording section of the service portal.
2. If the device placing the call has a headset, verify that the headset is not low on power. Some makes of headsets have a built in feature where the device will periodically beep to notify of low power when in use.
3. If calling a 3rd party conference line, verify if that conference service has a setting to play the tone you are hearing, it could be a reminder tone that the conference call is being recorded on that platform. I am not aware of any such feature with RingCentral Meetings or RingCentral Conferencing.
I hope this helps but if none of these pan out, please open a support case so this can be investigated further.