My 03 STR is coming along nicely and slowly but surely I'm going to have this thing better than new.

Current niggle is: rear parking sensors aren't emitting any sound or warning in the cabin.

I read some threads and thus checked for clicking and all four sensors are clicking as they should.

There is no audible sound inside the car. Not when passing reverse, never has been. I don't appear to have an on off switch.

Where is the speaker located? Seems the system.is being activated just simply isn't making sound. Ideas?

 

Yes it's a strange little speaker in the dashboard. Sometimes I have heard it called a "sounder".
Not common for them to go out so I can't guide you on where the speaker is. Also was not serviced separately so they had to find a used one.

Sorry for the weak bit of help!
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I believe the sounder unit is located under the rear "hat shelf" beneath the rear windscreen.

 

Couldn't find much

Also noticed my alarm makes no sound. Anyway these two could have been turned off?

 

Try this as those are not the speakers your looking for.
Those are your 2 sub woofers.

It's under the rear parcel shelf and you need to remove both sections of your rear seat.
Speaker Location
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Before you start tearing things apart... If your trunk has ever leaked (and what S-type has not...) there may be corrosion on the connections to the parking aid module. The module is mounted on the left hand side of the spare tire well in the trunk/boot of the car. I would recommend cleaning the contacts on the module and connector prior to disassembly of the interior...

 

Dangerous to say but mine hasn't leaked.

 

I was going to say one of the common faults with the parking sensors is water damage to the control unit in the trunk/boot.
I would also look at that first, it may need replacing.
The factory default is that alarm will make no sound when it is set and unset, other than the locks working. (I think this can be changed if you use the Jaguar software.)
Obvioulsy it should make a noise if it is set off!
Mellow