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nyryan2001

Why does engine noise come and go?

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nyryan2001

I understand engine noise is often created by a ground loop... ie all audio devices should be grouded and powered back to the same points for all of them.

But why is it that engine noise comes and goes? Some days I have none, and some days it can be strong when nothing changes? Why does it vary?

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shawndoggy

I'm sure david can provide a response with multimeters and ohms and stuff, but I'll say that some shatty rca interconnects have failed on me more than once with the same intermittent effect. Not that that IS the cause of your issue, but could it be a candidate?

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Earmark Marine

I agree with Shawn's statement about RCAs or RCA related terminations being the most common culprit in a come and go scenario. RCAs need to have their length times weight strain relieved against the effects of shock and vibration. The RCA shield needs to be a tight fit. Sometimes you need to compress the outer RCA connector a bit in a symmetrical manner. If you have an amplifier, EQ or signal processor with board-mounted RCAs, rather than chassis-mounted RCAs, then it's just a matter of time before you develop noise.

A tiny 3.5mm or other MP3 connecting cable can be very fragile and won't stand up to movement for long.

Depending on the wiring scheme and if the installation was done correctly, a ground loop can vary in potential according to the charge differential between the two battery banks.

The battery is your best noise filter so a lower charge level offers less filtering of AC components that are always present coming from an alternator.

One lose and intermittent ground can definitely do it. A multimeter measures continuity with very low voltage and is not a true indicator of behaviors when passing a ton of current. So it is better to measure a potential drop rather than resistance. Give crimped or soldered terminations a hard tug. Sometimes a factory termination will come right off.

A bad or corroded input sensitivity pot can do it.

A radio or other component can still get a good enough ground via an RCA above-ground shield to still operate while it is intermittently losing a harness ground. So it can be an intermittent molex connection.

A shorted speaker wire can do it. One shorted channel can induce noise into every speaker on that amplifier. All it takes is one tiny shorted single strand.

The number of speakers and zones with noise will tell you at what exact point in the signal path you have a problem.

And, it's true about using a multimeter and a few diagnostic tools to find the problem quickly rather than a protracted trial & error and speculation.

David

Earmark Marine

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MLA

The intensity of the noise may be tied to the alternator's output. Heavy loads = higher alt output = noise more noticeable. This may be why it varies from trip to trip. Stereo systems can be one big antenna for white noise thats already there. It gets amplified by the stereo electronics and reproduced by the speakers.

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Earmark Marine

^^^^ Very true MLA. And, multiple depleted batteries can create an enormous additional load on the alternator.

David

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