Whining about alternator whine

[jrubins]

My e36 (95 325is) has had an annoying alternator whine since I've had it. And I just. Can't. Take it. Anymore.
I've looked for the usual causes: bad rca cables, bad grounds, etc. I have an aftermarket cd player and aftermarket amp. I've redone the grounds to the cd and the amp, including trying to ground directly to the battery, nothing has worked.

Is there something particular to the e36 or some general trick that I haven't tried? I've gone through the forums and haven't seen anything.

Thanks!
JR


Sent from my iPhone using Tapatalk

[MarcoZandrini]

Alternator whine is typically caused by an issue with the grounds. Never ground any electronic module-amp, CD changer, etc.-to the battery. There may be a ground lug in the trunk above the left rear inner fender. Ground the trunk audio modules to that lug. If the lug doesn't exist find a metal brace or bracket. Drill a hole large enough for a quarter inch in diameter bolt, and the remove paint until you see bare steel. Bolt the grounds together there. Btw, ground cables need to be the same gauge wire as the power cables.

[M3 Pete]

bringing back this old thread because I have the same question. I grounded the amp as Marco suggested, using a large bolt that was under the rear deck, and grinding down to bare metal. Both power and ground use the same size cable.

I have not yet grounded the head unit, because I used an aftermarket plug that included a ground wire for the stock harness. Do I need to separately ground the head unit? .

[MarcoZandrini]

The ground is likely in the connector. The head unit works, right. It has to have a ground to work. However, the other end of the ground wire (always brown in a BMW) may not be tight at the grounding point.

[M3 Pete]

Yes, the head unit and the system works fine. If the stock ground wire is loose, and assuming I cannot find the connection point, can I just splice in another ground wire and connect it to the chassis?

Can I test the amp ground by running a wire to the battery grounding point? (the one right next to the battery)

[MarcoZandrini]

I highly doubt that the head unit ground is loose as you’ve noted that the it works fine. Is the amp the only other powered component in the audio system? If it is I’m betting the problem is at the amp. Don’t ground the amp to the battery as that’ll make the noise issue even worse. Try another grounding point in the chassis. Ground wires need to be kept as short as possible. Good hunting.

Is the alternator original?

[M3 Pete]

The ground wire is about 18 inches, it is 6 gauge. I was not talking about grounding to the battery, but the battery's grounding point on the chassis; is that a bad place? That grounding point is about 3-4 feet from the amp, and about a foot from the battery.

The only powered components are the head unit and amp. The alternator is original.

[MarcoZandrini]

I’d move the amp ground so that it’s closer to the amp itself. Also, check the resistance between that new ground point and the head unit ground. There should be zero resistance. The amp ground cable has to be the same wire gauge as the power cable.

[M3 Pete]

The amp ground is only 8-10 inches from the amp, the cable has some extra length for flexibility. The amp power and ground cable are the same size, made from a brand new 6 gauge battery cable that I cut.

When you say to "check the resistance between that new ground point and the head unit ground" do you mean connect a wire from the amp's ground point out to the head unit plug's ground wire, and put a multimeter in between? Or something else?

[MarcoZandrini]

Yup! Find out if there a resistance difference between the 2 grounds. Also, how old is the alternator? It can be the cause of the noise.