SOLVED: Alternator whine in RF channel only

[modernist]

Attached is a wiring diagram of my setup. 1986 325E. Alpine UTE-42BT. Upgraded from non-premium sound to premium speakers, converted from common to floating ground. Sounds fabulous when the car is off; rich, clear, detailed. When the engine is running, I'm getting loud alternator whine from the RF and very faintly from the LF. Rears don't whine at all.

My only idea is that the front negative cables are too close to the ECU and ABS boxes. Since they were the only wires I had to run, I decided to route them through the dash rather than tearing up the carpet. The RF negative runs through the space between the ECU and the dash, LF above the steering column, just below the cluster. I understand that this could cause interference, but would it sound like alternator whine? It does go up and down with RPM. All other wiring is in the stock locations. Checked and double checked all of my grounds, made sure the speaker chassis were not touching anything, plugs weren't shorting to anything .. stumped.

Edit: rerouted front negatives under the carpet. No change.

[modernist]

I just rerouted the front negatives under the carpet, still getting noise, the vast majority of which is in the RF channel. Both rears are completely noise free. LF has barely any noise. I checked everything when I had the carpet out a few weeks ago, didn't see any worn insulation or anything.

The RF speaker wires do run close to the main battery cable, but they ran there before as well. Does anyone have experience shielding an audio cable? Would it help? Wrapping it in another length of wire and grounding that?

[nrubenstein]

I can tell you that I need to work on that in the red car. Zero noise everywhere but the RF tweeter.

[TimeMachinE30]

Hood grounding strap in serviceable condition?

[modernist]

I'm pretty sure it's missing. The noise is not affected by volume or HU setting. Stays the same whether the antenna is connected or not.

Here's a recording of the noise, speaker by speaker.

https://www.dropbox.com/s/antkpchymszs9oj/Whine.m4a?dl=0

[modernist]

Switched L and R channels. Still whining on the right. Also, disconnected right tweeter. No change.

Help!

[TimeMachinE30]

Hood grounding strap in serviceable condition?

You said its missing?

[modernist]

Yup. I'm gonna try to make one tonight, see if anything changes.

[modernist]

Made a ground strap for the hood, put it on. Removed everything from g200, cleaned it up with a file. Reattached. Ran a brand new - cable on the right side, redid all splices. No change.

[modernist]

Would grounding the chassis of the head unit itself do anything? Would the main power line running near the RF speaker cause interference? I only ran into this after I converted it to a 4-channel floating ground system from a 2-channel common ground system. Literally only ran two wires, RF – and LF –. At my wits end.

Another theory: the crossover attached to the premium sound mid is picking up interference. Thoughts?

HELP

[bmwman91]

Are the new RF wires a tightly twisted pair, or are they separate/parallel? The stock wires are twisted together for a reason...when interference is induced by stuff like adjacent power wiring with large transient currents, the twisted pair of wires will pick up the interference equally (or closely anyway) which effectively cancels it out. If you pulled that wiring out and put in new separate wires then yes, it is possible that there is interference from the big power wire loom on the right side of the car. It sounds like you probably had to replace all of the speaker wires when you changed over to powering the speakers from the head unit?

The only other thing I can think of is that a capacitor in the crossover is crapping out and causing some serious distortion. Is the noise you hear coming from both the mid and tweeter or just the tweeter?

[modernist]

That makes sense. I have an early non-premium car, so it had the fader in the dash and common ground spliced under the carpet. The wiring to the back is totally stock, which would explain why there's no noise back there. The front positives are from the factory loom, while the negatives are new. They are not close together, nor are they twisted together. I'll try running new front positives as well, and twisting them to the new negatives.

The noise is in both the mid and the tweeter. It's still present with the tweeter disconnected. The noise is only present when the car is running; in ACC with the car off, sounds great. No distortion, has a warm, detailed sound.

[modernist]

Hope this works.

[bmwman91]

Good luck. Looks like you gave your drill a workout! (that's how I twist wires anyway)

[modernist]

Yup, sure did. Jammed one end of the wires in a door, went to town with the drill. Used the twisted cable for both fronts.

It worked! Thanks for helping a noob out. Whine is 100% gone.

Lessons learned: Mother nature thinks everything is an antenna. Twisted pairs are magical. Never cut corners.