Ford focus 58 plate audible tone while driving no warning lights and lasts for about 10-15 seconds and repeats every third of a mile

NOTE: The generic electronic module/central timer module (GEM/CTM) is connected to the ISO link and is diagnosed through the data link connector (DLC) with a scan tool.
There are five warning chimes and lamps the GEM/CTM controls: headlamps operating without the ignition on (chime only), door ajar (chime and lamp), key-in-ignition (chime only), driver seat belt warning (chime and lamp), and message center.


Audible Warnings Warning Condition Lamp Duration Audible Duration Audible Output Safety Belt 60 Seconds 6 Seconds Chime, 60/Min. 740 Hz Key In Ignition - Continuous Chime, 120/Min. 740 Hz Headlamps On - Continuous Chime, 240/Min. 740 Hz Door Ajar Continuous 1 Second Single Tone, 1000 Hz Message Center (Tone Request) - 1 Second Single Tone, 1000 Hz
When the is turned to RUN or START from OFF or ACC, the chime will sound for six seconds or until the safety belt is buckled.
The will turn on for 60 seconds or until the driver safety belt is fastened. Both the chime and the lamp turn on at the same time.
If the safety belt is buckled before the ignition switch is turned to RUN or START, from OFF or ACC, neither the chime nor lamp will be activated.
Anytime the is changed to RUN from START while the safety belt warning indicator is activated, the safety belt warning indicator will remain activated until either the timing sequence has been executed or the safety belt is buckled.
When at least one door is ajar and the key is in the RUN position, the door ajar cluster lamp is activated and remains on until all doors are closed. A warning tone will sound once any time the key is in the ignition switch and any door is open.
The key-in-ignition warning will sound when the driver side is opened with the key in the and the in OFF or ACC. It will continue to sound until the key is removed, the is closed, or the is in RUN or START.
The headlamp-on reminder chime will be activated if the headlamps or parking lamps are on, the key is not in the ignition switch, and the driver door is opened.
A single tone will be provided each time a ground signal is received from the message center. A one-second tone will sound for warning indications from the message center. A 100 milli-second tone will sound for each message center button depressed.

sound like your hand brake is staying on a bit

Does this only happen when the key is in the ignition? Try removing and re inserting key.

tun the fault codes to determine the possible fault sensor
indicates a crank/cam position sensor

key on engine off, does the airbag light illuminate then go out? or never seen? this is usually that the air bag light is not functioning as should so gives you an audible warning......

Ford Code Entry Instructions
Once the unit has been turned on the display will show ' CODE - - - -'
Press preset [ 1 ] repeatedly for the first digit
Press preset [ 2 ] repeatedly for the second digit
Press preset [ 3 ] repeatedly for the third digit
Press preset [ 4 ] repeatedly for the third digit

To save the code press the [ 5 ] key to accept.
The set should now operate

Ford  Code Entry Instructions

Once the unit has been turned on the display will show ' CODE - - - -'

Press preset [ 1 ] repeatedly for the first digit
Press preset [ 2 ] repeatedly for the second digit
Press preset [ 3 ] repeatedly for the third digit
Press preset [ 4 ] repeatedly for the third digit
 
To save the code press the [ 5 ] key to accept.

The set should now operate.

It maybe the seatbelt connection fault as some fords don't all have an illumination on dashboard

The secondary air bag warning is an audible fault format that consists of five sets of five tone bursts, with each set of five tone bursts separated by a five second quiet period. One tone burst cycle will consist of one second ON and one second OFF. This series of five activations is repeated every 30 minutes.
This will tone if the air bag indicator is inoperative.
Suggest to have the dealer or someone with a scan tool that will communicate with the restraint system retrieve codes.

did you clear codes out of computer codes will store in memory