PharoahTDI said:
I have the exact same issue on my 2000 Golf. I have replaced the headunit and there is no difference. I do notice that the pitch/loudness changes with the throttle.
Unlike the OP, I'm guessing your problem goes away when the radio is off? If not, do you have an external audio amp? What you describe sounds like alternator whine to me. That could indicate a bad ground or some other harness-related issue where stray RF from the alternator is finding it's way into the audio system. In the case of such a harness problem, probably the easiest fix for the noise is to put biggish inductors in series with each side of the power supply lines to the radio and amp (if there is one). That SHOULD cure the noise, but bear in mind other systems may be getting interference too which can cause erratic behaviors and you have not addressed the root cause--which may or may not become a bigger problem at some point. Allow me to give a couple of non-TDI examples:
There is a problem on a current model-year GM vehicle in which data communications from the audio system are throwing out JUST enough stray RF to cause false tire-pressure monitor alerts. Only a very small number of vehicles are affected, but a TSB has been issued in which the ground for the tire-pressure sensor is moved a few inches away from the radio ground point it currently shares. This has cured every instance so far. Here's the best part--GM engineering knew about the risk from past experience, but some knucklehead decided they could save a penny or two per vehicle by eliminating one screw and the labor to insert it. Every carmaker I've ever worked with (with the possible exception of Lexus) does crap like this all the time. Fortunately, in this case, the harness problem results in a mere annoyance.
Here's a more severe example. Many years ago I owned two consecutive Chrysler Horizon TC3's. Not bad little cars, but they nickle-and-dimed you to death as they got up in age. (Thankfully, Chrysler quality has made major strides in the last 10 or 15 years). These old Horizons had a braided wire strap for the alternator's ground. Corrosion eventually would cause this strap to lose conductivity and force the car's charging system to seek ground through some other path. In this case, the path of least resistance turned out to be through the right front wheel bearing. Over several hundred miles, the arcing across the bearing would trash it to the point that the wheel would wobble as you drove. On the way there, there was electrical noise a-plenty being made. I went through a couple bearings before we figured out what was going on. It seems unlikely to me that this kind of thing is happening in your TDI, but who knows?
I wish I could say just what was happening, but my experience with VW-specific systems is nil, and even if it wasn't it's almost impossible to say what's going on without actually inspecting your vehicle and trying a number of things to narrow the trouble down. Such is the nature of electronic systems.
If you (or anybody else here) are interested in the inductor fix I described, PM me. I have dozens of suitable parts in my junk box and will be happy to send you some for the actual cost of shipping--about $3.00. Hope that helps more than confuses.
dh