Well i found this technical bulletin from Jaguar, I can't copy the
illustrations but it does shed some light...

Audio - Poor Reception Diagnosis & Modification
S415-02

S-TYPE

DATE
10/02
MODEL
2000-02 MY
S-TYPE
VIN
L00001-M44997
Poor AM or FM Reception - Diagnostic Procedures - Modification
Procedure

Issue:

Some owners of 2000-02 MY S-TYPE vehicles may complain of poor radio
reception on both AM and FM.

This Technical Bulletin is designed to provide a quick check for
specific AM/FM reception interference issues.

With all diagnostic checks carried out and with a 'No Fault
Found' (NFF) situation, a roof-mount manual aerial service fix option
may be offered to reduce multipath (interference caused by signals
rebounding back of buildings) and improve reception.

Action:

On a customer complaint basis only, follow the workshop procedure
outlined in this Technical Bulletin.

S-TYPE - AM/FM AUDIO INTERFERENCE DIAGNOSTIC CHECKS
VIN L00267 TO L77674
Check the history of vehicle to ascertain whether actions described in
Technical Bulletin S415-01 (AM reception interference) concerns have
been carried out on vehicles between VIN L00267 to L77674. If not do
this first.

If there is no AM, check that the red/yellow wire is present between
FC40-4 and FC71-7. Check all coaxial cable connections, check the FUBA
connections and make sure the mounting is good since it is also a
ground. Check the harness between the FUBA and the rear glass for
opens or short circuits. Check the rear glass terminal, check that the
black/white wire is to the top and check the rear glass for shorting
between the pins.

AM/FM RECEPTION ISSUES VIN L77675 TO M44997

AM-Specific issue

Concern - Standard Corporate Protocol (SCP) network interference,
evident with the ignition in auxiliary position I, and engine run
position II. Noise does not increase with engine RPM. The noise
exhibits itself as a ticking and is primarily due to inadequate
screening of the antenna circuitry. At VIN M20244 the antenna module
to screen harness was screened. Between VIN L77675 to M20244, if this
concern is identified, check the antenna lead to see if it has already
been replaced with the latest screened condition. To check, carry out
the following workshop procedure.

1.    Remove the left hand side rear quarter trim panel to expose the
Antenna Module. (See Workshop Manual, JTIS CD ROM, section: 501-05)

2.    Carefully unclip the antenna harness (As indicated at 1
Illustration 1) from the screen connections and disconnect from the
antenna module. (As indicated at 2 Illustration 1)

3.    Carefully pull back the harness insulation tape at the connector
and check to see if there is a braided cable situated between the two
harness cables. If not fitted, install new modified cable, part
number: XR8 36434 (Illustration 2).
Note: When refitting the screened lead to the terminal, the black wire
with white tracer should be connected to the upper screen terminal.
Should the concern persist with a screened harness fitted check the
antenna module ground circuit.

4.    Check if fixing bolt securing the antenna module bracket to the D-
post is tight. If loose tighten to 6.2 Nm.

5.    Disconnect antenna module coax connector from the module. (Using a
suitable multimeter with appropriate ohm setting). Connect one probe
to ground point on the antenna module and the other probe to the local
ground point on the rear bulkhead behind the seat squab trim. (As
indicated at 3 Illustration 3)
Note: Do not connect the multimeter probe to the fixing bolt for
antenna module.
6.    If a high resistance reading is present a concern with the antenna
module ground connection exists. The ground path for this is through a
dedicated cage nut on the rear bulkhead. Loosen the fixing bolt to the
cage nut and re-torque to 6.2 Nm. to re-establish the correct ground
path.
NO AM RECEPTION BUT POSSIBLY SOME FM STATION COVERAGE

Assuming the radio unit is powering up and operating correctly, the
fault could be caused by the loss of 12-volt supply to the antenna
module.

1.    Using a suitable multimeter, check voltage at electrical connection
CA2O at the antenna module, if there is no voltage, check voltage at
the intermediate electrical connection FC4O pin 4. This electrical
connector is located at the left hand side of the facia assembly
behind the A-post cover. If there is voltage at FC4O pin 4 electrical
connection then the fault is within the rearward electrical harness
section to the antenna module.
2.    Check all electrical terminals and wires are secure and connected
correctly. If satisfactory the fault is within the electrical harness.
3.    If there is no voltage present at FC4O pin 4 remove radio and check
voltage output from electrical connector FC71 pin 7 (on some wiring
diagrams this connector is FC73 pin 7). If there is no voltage at FC71
pin 7 check battery/ignition inputs and fuses.

Circuitry details as shown.

AM/FM Combined Issues

Concern-Overall poor radio reception, increased multipath issues on FM
broadcasts.

1.    Remove left hand side C-pillar trim to expose antenna module. (See
Workshop Manual, JTIS CD ROM, section: 501-05, SRO 76.13.73).
2.    Carefully unclip the antenna harness from the screen connections.
3.    Using a suitable multimeter with appropriate ohm setting selected,
place one probe on the upper screen stud and the other probe on the
lower stud. The expected reading should be '0' ohms. If there is a
high resistance reading then check for solder splash between the two
screen studs or screen sealant on the studs. If contamination is
present this should be carefully removed with a suitable blade or
implement.
4.    If there is interference only when the Heated Rear Window (HRW) is
switched on, affecting AM frequencies and weaker FM bands, possibly
caused a break in the circuit of the HRW. Install new screen.
FM Issues

Concern-Poor radio reception all frequencies.

1.    Remove left hand side C-pillar trim to expose antenna module. (See
Workshop Manual, JTIS CD ROM, section: 501-05, SRO 76.13.73).
2.    Carefully unclip the antenna harness from the screen connections.
3.    Using a suitable multimeter with appropriate ohm setting selected,
place one probe on upper screen stud and second probe onto heated rear
window buzz bar, the reading should be 6 ohm plus or minus 1 ohm. If
the reading is higher than 6 ohm this will indicate that there is a
break somewhere in the screen element circuitry.
Install new screen.

Note: If the screen is damaged it is not covered under warranty.
General Information

Concern-AM/FM poor radio reception.

If the customer has a non-Jaguar phone, and glass whip aerial
installed on the rear screen. The location of the aerial, if in
contact or close to the rear screen elements could compromise radio
reception signals. Even if the glass whip aerial is disconnected, the
actual presence of the aerial on the screen could be a factor.

Note: If any of the diagnostic checks require repair, carry out a
separate warranty claim. This Technical Bulletin only covers the
interference diagnostic checks and the installation of the roof
mounted manual aerial.

Parts Information

Warranty Information:

Warranty claims should be submitted quoting the information in this
table.

This will result in payment of the stated time and, where applicable
parts/miscellaneous expense codes as listed.