GM Bose System High-Frequency Noise!

Guys, I was able to "assemble" an oscilloscope consisting of a studio quality condensor microphone, analog-to-digital converter, and laptop computer with some trial software that displays graphs of the entire audio spectrum (20-20,000 Hz) in numerous ways that can be captured and saved. I'm just finsihing tests and will try it in the car tonight when all is very quiet. Man, I hope this works! I'll post my results. Again, thank all of you for your time and excellent suggestions. Brent

Wasn't able to isolate only the high-pitch noise with the oscilloscope but was able to record the noise successfully to digital tape which I transferred to my computer and increased the gain. It is absolutely audible now. There is no way anyone can listen to the recording and claim they don't hear it now. Also, had an independent audio technician (sent by the BBB) come out and listen to the radio. He confirmed the noise and will be reporting his findings back to the BBB. Just hoping we'll get somewhere now - FINALLY. (This has been going on since early January 2005). Brent

Good stuff. Hopefully it works out for you.Certified Security Specialist

Always check info with a digital multimeter.

I promise to be good.

Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.

Thanks auex. I appreciate your help and concern. Brent

The problem sounds like it is in the routing of the wires or in their connection to the various components. The noise may be generated by a bad connection from the connector plug pins to the mating pins in either the radio, rear seat audio control unit or the amp. Has the dealer installed and rerouted in a different path the shielded audio lines between the radio and rear audio controls and then to the amp? There are also a couple of GM service bulletins they can refer to that cover noise only on the rear speakers. One details what I just mentioned and another lists a possible problem with the transfer case module ground. The other thing to note is any characteristics of the noise. You mentioned that it didn't increase with RPM. Does the noise go away if you turn the radio off with the engine on? Is it affected in any way by using other accessories in the vehicle? Are you sure it is noise coming from the speaker and not from the powertrain or drive belts? Troubleshooting noise is not always easy. Be patient and GM will fix it once they etablish what the noise is and how to duplicate it.sparky

Sparkle, The dealer has replaced every component of the radio system and has rerouted the wires, replaced connectors, and installed noise filters for the power and antenna. I'll have them check for the service bulletins you mentioned as I hadn't heard about those previously. The noise is always present when the engine is running AND the radio is on. The only other time the noise is heard, with the radio off, is when a warning tone (fasten seatbelts, low fuel, etc.) comes on as it activates the radio system to sound through. When the tone ends, the noise disappears (provided the radio is still off). It is absolutely a radio/speaker noise. Thanks for your thoughts. Brent