My sound symposer works for the first 5 minutes when I start then stops working. What could be the cause

The sound symposer system generates an artificial engine noise. The system consists of a small resonator box that is connected to the air intake and a plastic hose that directs the sound into the cabin. The small resonator box contains a flap/membrane that resonates at a frequency of somewhere between 250 and 450 Hz. On the 1.6 ECOboost the system is tuned to sound "discreetly" at low and medium RPM's and to sound "sporty" at high RPM's.

Since it is a full "mechanical" system it does either work or not. There is basically nothing in between. The only part of the system that can fail is basically the flap/membrane but I have never seen or heard of it failing. 

It is however completely normal for the sound symposer to sound a bit louder while the engine heats up because during the warmup stage the engine idles at a higher speed which also affects the frequency.

This made me recall some discussion from years back as to whether all 1.6 Ecoboosts got this, or if it was just certain years and/or trims.

Mountune used to offer a symposer as an option with their MP200 upgrade for the Mk 3, the extract below is from this Piston Heads review at the time:

https://www.pistonheads.com/features/ph-features/driven-ford-focus-zetec-s-mountune-mp200/26732

"The package is available with an optional ‘sound symposer’ – a similar tube of tricks to the one fitted to the Focus ST. This gizmo is essentially a pipe which ‘feeds’ sound from the intake manifold through to the bulkhead. It has whiffs of artificiality about it, but this is no synthesized engine note being played back through the stereo. We’d recommend it, as for £50 extra it completes the car, adding a snarly little backing track to your B-road antics. Without it, the standard engine note still feels a tad anodyne."

 

On 1/24/2025 at 6:58 PM, JW1982 said:

The sound symposer system generates an artificial engine noise. The system consists of a small resonator box that is connected to the air intake and a plastic hose that directs the sound into the cabin. The small resonator box contains a flap/membrane that resonates at a frequency of somewhere between 250 and 450 Hz. On the 1.6 ECOboost the system is tuned to sound "discreetly" at low and medium RPM's and to sound "sporty" at high RPM's.

Since it is a full "mechanical" system it does either work or not. There is basically nothing in between. The only part of the system that can fail is basically the flap/membrane but I have never seen or heard of it failing. 

It is however completely normal for the sound symposer to sound a bit louder while the engine heats up because during the warmup stage the engine idles at a higher speed which also affects the frequency.

Is there a way to inspect the mechanism? I can hear it when I restart the engine whilst it's warm and I've noticed that for some reason when the start stop turns off automatically the symposer stops working too