Symptom

Antenna signal condition

Source

Only a buzzing sound from the speakers

• There is no broadcasting wave.

• Signals from antenna to audio unit/car-navigation unit are not transmitted.

• Electric noise caused by the operation of internal circuit from audio unit it self

• Atmosphere noise

A buzzing or crunching sound and normal sound produced at the same time from the speakers

• Though signals are transmitted from antenna to audio unit, electric noise from other sources is larger.

• Electrical noise caused by operation of electrical component on vehicle

• Electrical noise from high tension wire, transformer substation (factory), electrical feeder line (street car), or motorcycle.

A thumping sound and normal sound produced at the same time from the speakers (FM only)

• Noise occurs due to radio wave environment at specific places (e.g. in valleys between buildings). Noise varies when own vehicle or surrounding vehicles moves. (FM only)

• Interference between direct and reflected waves of FM signals causes noise (Multipass noise).