Identification Of Noise Source

WARNING: This page is about a different car, the 2004 Toyota Camry Solara. However, it is still accessible from the selected car via links, so may be relevant.

RADIO WAVE BAND
The radio wave bands used in radio broadcasting are as follows:

Fig 1: Radio Wave Band Table
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

LF: Low Frequency

MF: Medium Frequency

HF: High Frequency

VHF: Very High Frequency
SERVICE AREA
1. There is a great difference in the size of the service areas for AM and FM broadcasting. Sometimes an FM stereo broadcast cannot be received even though AM can be received very clearly.
  FM stereo has the smaller service area, and it also picks up static and other types of interference ("noise") easily.
Fig 2: Radio Service Area
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RECEPTION PROBLEMS
HINT:

Besides the problem of static, there are other problems, such as "phasing", "multipath" and "fade out". These problems are caused not by electrical noise but by the nature of the radio waves themselves.
1. Phasing
  Besides electrical interference, AM broadcasts are also susceptible to other types of interference, especially at night. This is because AM radio waves bounce off the ionosphere at night. These radio waves then interfere with the signals that reach the vehicle's antenna directly from the same transmitter. This type of interference is called "phasing".
  
  Fig 3: Identifying Radio Phasing
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Multipath
  Interference caused by reflection of radio waves against obstructions is called "Multipath". Multipath occurs when radio signals emitted from the broadcast transmitter antenna are reflected against tall buildings or mountains and interfere with other signals which are to be received directly.
  
  Fig 4: Identifying Radio Multipath
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
3. Fade Out
  FM radio wave tends to be reflected against obstructions such as tall buildings or mountains because FM frequency is higher than AM. For this reason, FM signals often seem to gradually disappear or fade away as the vehicle goes behind those obstructions. This phenomenon is called "fade out".
Fig 5: Identifying Radio Fade Out
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NOISE PROBLEMS
1. It is very important for technicians to clearly understand a customer's claim about noise. Use the following table to diagnose the phenomena.
Fig 6: Diagnose Phenomena Table
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

If the condition when the noise occurs does not meet any of the above, find out the cause based on "Reception Problems". Refer to the description about multipath and phasing mentioned previously.

Identify the conditions under which the noise occurs, and check the noise filter on the relevant part.

Fig 7: Noise Source Table

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

CONDITIONS UNDER WHICH NOISE OCCURS

Conditions under which noise occurs	Noise type
Noise occurs when the brake pedal is depressed.	Stop light switch noise
Others	Static electricity stored on the vehicle

Reference:

Make sure first that there is no noise from the outside. Failure to do so makes noise source detection difficult and may lead to a misdiagnosis.
Noise should be removed in descending order of loudness.
Tuning the radio so that no station is received makes the noise more noticeable, making the recognition of the phenomenon easier.