Sounds like interference from an electric motor. Eggman's right, try a pocket am radio as a 'sniffer'.
Your SDA radio, it's aftermarket?
Keep in mind most radios have their AM antenna built in to the radio enclosure. The external antenna is typically FM only.
It's been this way for years.
2018 Mirage G4 1.2 ES CVT
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View my fuel log 2017 Mirage G4 ES CVT 1.2 automatic: 42.0 mpg (US) ... 17.9 km/L ... 5.6 L/100 km ... 50.4 mpg (Imp)
Is it on AM, FM or both? How good is reception generally? Does the situation change with the ignition turned all the way off?
Very important: Have you added anything whatsoever electronics to the car? If yes, have you removed it to check yet?
Done that, there are two equally important things to check out next when searching for static causes:
A) grounding of the radio itself:
The actual ground connection of the radio to the chassis must be electrically perfect. Just connecting the antenna cable to chassis on the antenna side is good for the antenna, but not enough for grounding a radio. Below the radio, there is a horizontal metal tube/brace across the underside of the dash. That brace is connected to the chassis near the front door hinges on either side, and offers a good electrical ground. You could connect a short flexible cable to that tube, the other end leading to the metal case of the radio. Removing (unclipping) the glovebox helps getting better access.
B) grounding of the antenna at its base:
The antenna is an active typ, meaning it has a small whip and an electric buffer amp. To improve the grounding of the antenna, the shield of the coax leading away to the radio base, must be connected from a point right at the base of the antenna, to the chassis via a short and not too thin cable. If that conection is bad, you get lots of noise right there. On mine, I removed the rubber seal on the upper part of the hatch for better access to the underside of the antenna, and put a proper grounding in place. I had to remove a little of the outer insulation of the coax to be able to swiftly solder a grounding lead to it. My reason for doing that was, I like listening to BBC Radio4 on 200kHz long wave while driving in central Europe.
When those two points have been taken care of, you will probably likely have things working. If not, we can continue from there.
Last edited by foama; 01-21-2018 at 09:37 AM.
AM radios are the most susceptible to noise by nature due to the way electromagnetic energy interacts with AM signal transmission. FM transmission was invented due to this fact.
You may have to do some probing. Process by elimination, the USB power adapter is now ruled out. Next thing is that you do as I suggested in my previous post to eliminate the possibility that the noise is aggravated by AC ripple (harmonics) coming from the alternator. You may have to install inductive filters to the power lead in this case. Look out also for ground loops.
Audio Interference - AM - Car Radio
Interference on AM and FM Radios
Curing Radio Noise
Noise suppression guide
Ground Loops: Car Audio Hums and Whines