Has anyone encountered an issue with their cars alternator being amplified through car speakers?

Posted 14th Apr 2023

I have a DAB device hooked up to my car, to give me Bluetooth and in car calls etc, as my car is an 05 plate. The trouble is, when I have it on Bluetooth, I can hear the cars RPM through the speakers. When I switch the DAB off, the noise goes away. I read I need a noise filter to stop noise from the alternator getting into the head unit and my speakers from the power cables. Is this an easy fix, and how cheap can I get a noise filter please? Apologies if I've got anything wrong in my description. Thanks in advance.

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Timbonagasaki
14th Apr
Maybe you need a suppressor. They used to have them fitted in the ignition systems of really old cars to stop interference.
Toon_army
14th Apr
I'm a little lost, have you got some kind of FM transmitter plugged into the cigarette lighter?
I've had loads of them and never heard one do the revs thing, maybe send it back or try another one?
DealHub Author
14th Apr
Yeah, it's plugged in via USB in a cigarette lighter dongle Toon, which is providing power to the DAB. I installed an AUX cable behind the cars stereo last year, and left that in the glove box to plug into my phone until needed. Now it's plugged into the DAB unit permanently on my dashboard. I don't think it's a faulty unit to be honest, at least I hope not. It's really baffled me, and ruining my Supertramp playlist, namely my favourite album Supertramp live in Paris 1979 (edited)
Willy_Wonka
14th Apr
I should imagine its an earthing issue on the DAB aerial. How is it earthed? If it is heavily painted the magnet will stick but won't be earthed.
DealHub Author
14th Apr
It's earthed under the headliner to the frame, unless it's came loose? (edited)
Sprograt
15th Apr
As Timbonagasaki says you need a radio suppressor that will stop interference coming through the car speakers. They look like this
Drekly
15th Apr
Yes in the 70's in my triumph herald.
Didn't know this was still an issue .
slimy31
15th Apr
Personally I'd say you have an earth loop. If you have powered the DAB through the USB bluetooth, then both the DAB earth and the USB earth are competing. Rather than check if the DAB aerial is earthed, I'd actually try disconnecting it. It might lose a bit of DAB reception but I think the whine will disappear.

Or you could try temporarily powering the DAB off a power bank, again that would break the connection between earth loops.