Problem with alternator whine through aux when audio source is connected to 12V power

I am having an extremely frustrating problem with alternator whine whenever my audio source is connected to 12V power. My car is a 2008 Boxster S w/ Bose and the CDR24 radio. I have added a Dension Gateway 500 to add aux input and iPod input, and am attempting to use an Anker SoundSync ( https://www.amazon.com/Anker-SoundSync-Bluetooth-Streaming-Multi-Point/dp/B0176G5TRO ) for bluetooth integration. My problem is that any time a source is connected to power from the car I get what I believe is alternator whine (a high pitched whine that increases in frequency with the engine). For example, iPod input and aux input (when nothing is connected to a power source in the car) has no whine. However, when I plug my phone into a car charger (I have tried the center console and passenger footwell plugs) and plug the phone into the aux input I get an alternator whine. These are things I can live with though. I don't mind keeping my phone charged to use the headphone jack. The thing that is unbearable to me is the fact that I get the same alternator whine from my bluetooth kit, but this is something that requires constant power to work. I have tried the USB port on the Dension unit, both cigarette lighters, and even attempted hardwiring a 12v to 5v stepdown with USB output for power, and they all still have alternator whine. I have also tried adding a ground loop isolator, which seems to have little effect on this problem. Does anybody have any solutions to this extremely frustrating problem? I currently have it plugged into stepdown that I hardwired, which has the least alternator whine, and I am getting power from the switched auto-dimming mirror fuse, and I am grounded on that small bolt to the left of the fuse box when you have the entire fuse cover removed.

well, I'm no expert, but it seems to me that if multiple devices are now producing alternator whine, you have increased alternator noise on your 12V line for some reason. I've used a variety of bluetooth devices on my non- bose CDR24 system without issue. I guess something could be funny with the grounding somewhere or maybe you have a bad diode in your alternator (which would add noise). Normally the car battery damps out the alternator noise - presumably you have a good battery hanging on the 12V line and all connections are sound. An interesting experiment would be to cover the center pin of the charger with tape and plug it in so only the ground connects (not the 12V) and see what happens. If you still get noise then that would point to a grounding issue. Hopefully someone else will have some ideas. Good luck.

I'll give the USB experiment a try tomorrow morning. Car audio/electronics are not my forte, so I honestly didn't consider the possibility of a bad battery. In my world I just assumed that if it started the car, the battery was probably fine. It looks like my battery is a little over 5 years old (50/11 stamped on negative terminal), which seems to be towards the ends of most batteries' lives. Is it possible that age has made it lose that damping ability?

It seems your Bluetooth receiver device has poor isolation to current noise. Have you tried using a USB battery between the power source and the Bluetooth receiver device? That could potentially isolate the noise. Talking about something like this: https://www.amazon.com/Anker-PowerCore-Lipstick-Sized-Generation-Batteries/dp/B005X1Y7I2

If the car is starting fine then I don't think the battery is the issue. I spent a few years designing car radios for Ford, but my focus was providing adequate filtering within the radio, not fighting issues on the car. Since you have multiple devices having the problem, something somewhere must be wrong, and the grounding experiment may provide insight. (Hopefully someone with a similar issue will chime in on this thread.)

Yeah the car is starting fine. I gave the grounding experiment a try and that does seem to be the problem. I tried it with my phone (since the bluetooth thing obviously needs power to work), and still got the whine. Could this mean that the battery isn't being grounded properly? My Boxster is new to me, so on top of my lack of knowledge about car electronics, I know even less about Boxster electronics haha. I did try using something like that for power once to troubleshoot (trying to make sure that the bluetooth transmitter actually worked), but I haven't tried charging it while any of my devices are plugged into it.

Ugh, grounding problems are not fun. Maybe the radio is not grounded properly, and when you connect a device to a USB charger the radio gets grounded through the USB ground and current flows through the aux/USB cable ground which modulates the signal wire and you get noise. But obviously the radio must be grounded or it would not work, but maybe it is getting grounded by things plugged into it, like the antenna. Per the attached diagram, it looks like terminal 31 should be grounded to the "left side of middle support frame" (see bottom left of diagram). Not sure where that is exactly, but maybe the connection is loose/missing.

I'm not seeing a diagram attached anywhere, but I'm new to this forum. Am I missing a link or something on your post with a diagram? And I believe that the radio is grounded properly because I tapped the radio ground wire to ground my dension unit (which also turns on and works). Thanks for all of the help so far, by the way. I really appreciate it.

Sorry - diagram attached. Is it possible that when you tapped the ground wire you inadvertently broke the connection to the CDR24 ? I don't have any experience with the Dension unit.

It's possible, but I don't think it's very likely. I used one of these http://cpc.farnell.com/productimages/standard/en_GB/42403228.jpg . I'll try changing the ground of the Dension when I get a chance.

Yeah, I forgot the aux/iphone connections are to the Dension unit, not the CDR24 (which of course does not have those inputs). Seems more likely it is something funny going on with the Dension unit ground-wise. Maybe you need help from someone more familiar with Dension.

True. Now that I think about it, the ground wire that came with the Dension was very long, so I ended up just coiling it. After all my research for this problem I've come to realize that that can cause problems for a ground, right? I'll try shortening the wire and choosing a new ground location. Thanks again for all of the help!

I've had the exact same problem. iPhone works fine but if you connect via rca plugs engine noise. Because of that, I don't use the rca plugs aux input. To bad as the unit is not cheap.

That is disappointing. aggielax7, can you ground your step down to the same bolt the CDR-24 is grounded to? I assume the Dension unit is picking up ground solely from the CDR24 , so I think if your charger used the same ground the CDR24 uses you would minimize or eliminate the issue.

It never hurts to shorten a ground wire, but I doubt the excess length is the issue.

I'll definitely give those suggestions a try shortly! I'm taking a tinkering break until the weekend.

So it appears the basic issue is the dreaded "ground loop", where different items are grounded to different grounds in the car. The car grounds are very noisy due to all the electrical items running, so any time you ground items to different areas, then connect them via an aux cable, you end up with noise conducted on the aux cable ground which gets coupled onto the signal wire and you hear alternator whine. The only hope is to either go optical, like Porsche does for the CD changer, or go to a star configuration, where all grounds are coming off the same point. Having never installed a Dension box I may be weak here on my understanding, but if you connect the box by tapping into the ground wire going to the CDR24 , and don't separately ground the Dension chassis by, e.g., screwing it to the car's chassis, that connection should be OK. Your USB charger must also tap the CDR24 ground wire (only). However, in the original post aggielax7 mentions trying the USB port on the Dension box and still having the issue, which I find very confusing. If a single ground point is used for everything, there should not be an issue, with the grounding anyway.

Now that is an interesting thought that I hadn't considered with the Dension. Mine is mounted behind the stereo, so it is touching the metal frame that holds the stereo. However, that sounds like it might be what the stereo is grounded to as well. This weekend when I get around to messing with these connections I'll try moving the Dension box somewhere where it isn't contacting any metal.

My stock '09 car does this. It's prob not related to the aftermarket stereo. It's poor grounding. If I use aux in I have to unplug power to my phone. Wish there was an easy fix

Crutchfield has a nice guide to troubleshooting noise in audio systems. https://www.crutchfield.com/S-eYFM7...-eYFM7SQXKiM/learn/learningcenter/car/noise_suppressors_installation_guide.html