Hi Everyone

2008 G35x Base here

Anyone ever heard their alternator buzz/hum when the key is on the ON position without the engine running? Its not super loud, but easily heard in a quiet garage. I checked voltage, I'm getting 13.92v with the engine running. I checked all my major grounds and made sure they are all secure and clean. The information I've found so far indicates that this buzz/hum does not affect the operation of the alternator and will continue to function normally. The main issue with this is that I have an aftermarket stereo setup and that Buzz/Hum is making it to my car speakers. I've tried every filter I could find on Amazon with none of them working including RCA and power filters. Hum goes away when headunit is muted. I've tracked the hum to my door speaker amp, ive tried different amps, same result. The hum is getting sent to that amp. I have 4 gauge power and ground cables. I also upgraded my battery ground cable to 4gauge to match. If I disconnect RCAs from the amp the hum in the speakers goes away. And I know its that alternator causing this hum because its the same exact noise I hear from the speakers. Identical tone/frequency. Anyone have any advice? Or do you think I should just replace the alternator despite it most likely being mechnically fine. I'm out of ideas. Thanks.

 

Try a clip on ferrite choke to see if you can absorb it that way.

You're getting noise induced onto your electronics somehow.

So this sound only happens when the ENGINE IS RUNNING correct?

 

Nope, It's when the engine isn't running and the ignition is set to ON.

 

You don't mean you're hearing a buzz coming from the physical alternator bolted to the engine, do you? With the engine off the entire car should be running on DC power so there shouldn't be any AC happening anywhere which would cause a buzz or vibration - unless you have a 12vDC- 120vAC converter wired in somewhere. Or if one of your amps is doing something like that.

You mentioned that you've changed every component of your sound system - but have you tried any alternative signal cables? Your amp and speakers are quiet when you disconnect the RCAs so that makes me wonder if it's THAT cable which is introducing the interference. You might want to try an alternative, well-shielded wire from head unit to amp - even just test it by running it through the cabin. You didn't say where your amps are located but the longer the run the more important the wire's shielding is.

I guess it's possible that some of our car's black boxes might have processors in them which create RF interference so sometimes the audio cable routing needs to be adjusted to avoid those noise sources. I've also heard about some LED replacement bulbs causing RF problems. Just some ideas.

 

Hi Thanks for the reply. Sorry if I'm not being clear. I only hear the buzz when the engine is OFF but the ignition is set to ACC/ON. I have also tried different RCA cables and I would run them down the middle of the car loosely not even close to any power wires and I still receive the same result. I definitely know that buzz is reaching the RCA cables via the amp. As I said earlier, the buzz from the alternator is the literal same exact tone/frequency I'm hearing in my speakers. That's how I know.

 

If it's only when the engine is off then it's definitely not the alternator since it's not even spinning.

I would try the ferrite choke first since it's easy, then shielded wire (make sure to actually drain it to ground).

You could also just have a loose ground on the head unit (or they grounded on something they shouldn't have) and it's building up a charge somewhere, typically an aftermarket HU would be grounded to the ECM ground which is located behind the glove box, you might want to just take it directly to the battery negative though.

One way to isolate the noise is to disconnect the battery, Use a second battery connector and temporarily run a new circuit up to the head unit and amp, (basically powering up the stereo while the entire car is disconnected). If you still have whine then it's DEFINITELY not something else in the car since the entire vehicle is deenergized.

If it's quiet while the rest of the car is unplugged then you just start a process of elimination by removing fuses until the noise goes away, then you know which circuit is the culprit.

If it's still making noise with the whole car deenergized then it's just bad stereo equipment.