Hello & Welcome,
Are you getting any sounds from your Nuvi at all, like attention tones or sound when you touch the screen?
Sorry for the delay.
Please try the following and let me know what happens.
Check the audio output setting on the nuvi. There is a possibility that the FM Transmitter setting has been turned on or that the device has been muted.
To check the audio output setting:
If that doesn't change anything, you might want to try a "Master Reset".
To do a Master Reset on the nuvi® 6xx series device:
Note: A master reset will erase all waypoints or favorites and will restore your unit to the default factory settings.
The device will automatically reset. Please follow the on screen prompts on the nüvi and when completed place your device in an area with a clear view of the sky until it acquires satellites.
Please let me know what happens.