A mystery involving a phone charger, an auxiliary input and a whistle...

[Anthony28]

I have already accepted that my little fiesta mk6 is going to have to be somewhat of a project top get it up to something i am happy with but it seems on top of the current issues, a new one has cropped up that i could use your advice on. 
After i bought the car i had an auxiliary input installed (official ford part) i have used the input extensively with no problems, aside from a slight crackle from passenger door speaker. This i have put down to a faulty speaker, another job entirely. Anyway, yesterday i plugged my phone in to both the aux in and then the USB charger cable which in turn was plugged in to a usb adapter that fits in the 12volt supply (cigarette lighter). Almost instantly i noticed the sound was slightly distorted and crackly. Still relatively clear but not 100%. The other thing is, when accelerating i can hear a whining/whistling sound from the engine. The higher the revs the louder the noise. If i unplug the charger the noise instantly goes away.

Any suggestions.... alternator issues perhaps?

[DB617]

I've got a similar problem with music played through a bluetooth-FM retransmitter on the 12v socket. I also suspect that everything on my aux belt has been damaged, including the alternator, so you could be onto something there. Then again, my Doblo van doesn't fare much better with retransmitters so I guess alternators produce pretty dirty DC anyway.

[Jonro2009]

Try using a different USB cable, preferably the one that came with he phone. 3rd party leads are notoriously bad for doing strange things, if you don't have the standard cable that came with the phone then try putting a Ferrite Core filter on the cable and see if that helps. https://www.ebay.co.uk/i/122248857939


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[Anthony28]

It is the original cable. The 12v USB adapter that I bought was only a couple of quid on eBay. I'll try changing that see if it helps 

[ToXIcG]

Sounds like it might be a grounding problem, I had the same kinda thing when using a bluetooth to aux adapter that was plugged into the lighter socket for power.

After doing some research it turns out that apparently sometimes car manufacturers don't properly ground both the aux and lighter socket to the same place so it causes this problem.

Supposedly a ground loop isolater will fix this issue (I don't know about the engine noise though)

Here is one on Amazon

I have ordered the one above and it is coming soon, hopefully it will sort the issue.