Engine interference on radio!

[mariner]

Hi all. Have just got round to wiring back up 4 additional speakers I have under my rear seat. They are connected to an amp which is in turn connected to the radio and to the leisure battery for power.

Hasn’t been wired up for a couple of years and I have moved the leisure battery so had to splice in some additional cable between the amp and leisure battery so it would reach.

I’m getting a sort of whistle like interference when using the radio that goes up and down with the revs on the engine. If I unplug the rear speakers and go back to using just the front two that run direct from the radio then no probs.

Also have solar, zig and vsr running off leisure battery connectors although I had this same set up previously without any problem so unsure what may have changed to cause an issue.

Any obvious areas I should be investigating? Thanks

[Robsey]

I am assuming that because of the addition of wiring closer to the engine bay of the vehicle, it is assumed that these speakers are picking up interference from the alternator.

The usual cure in the past has been the fitment of a supressor (capacitor) between a contact on the back of the alternator and the alternator body.

Motor interference whine was very common on 80s vehicles.

[colinthefox]

I am assuming that because of the addition of wiring closer to the engine bay of the vehicle, it is assumed that these speakers are picking up interference from the alternator.

The usual cure in the past has been the fitment of a supressor (capacitor) between a contact on the back of the alternator and the alternator body.

Motor interference whine was very common on 80s vehicles.

I was going to say that I had a similar noise when the alternator regulator brushes were worn and sparking, just before it failed. A new voltage regulator cured it. Pop the regulator out and have a look at the brushes. If one is very short, that may be your problem.
 

[mariner]

Thanks both.

Speakers are where they have always been but the leisure battery and associated wiring is now in a cupboard alongside the bed rather than under passenger seat - from what you are saying it sounds like this move could have caused the interference. I get it both with the radio and when I use other functions such as Bluetooth to link it up to my phone and play music - if that’s significant at all?

Currently back to just front two speaker whilst I take your advice and check out the alternator.

[keynsham1]

I had a similar problem which turned out to be the earthing of the aerial. The aerial screen braiding on the wire to the radio seems to need a good earth connection at the aerial where it attaches to the body. The nut and bolt was loose on my aerial and when I tightened it up, the noise went away. An additional earth on the casing of the radio unit wouldn't hurt either!

[Rosie n' Jim]

I would look at the audio feed from radio to amp. It's a weak signal that is amplified,  slight interference will also be amplified.  Moving you wiring may have bought the cables too close. You may find simply moving the audio cables a few inches would help.