PWM Sweep Noise when in Auto or 4WD

tbully said:

Hello All -

Brand new 2015i Denali owner here.

We have a little snow in the Detroit area tonight so I had the chance to try out AWD / 4x4. I thought about putting this in the drivetrain section but I think it's more of an electronics issue.

First, I have very sensitive hearing and am lucky (?) enough to be able to hear well at the top of human range.

I noticed when in Auto or full-time 4x4 there is a strange PWM sweep noise coming from behind the instrument panel when varying throttle input (cruise also does it).

You can also create the noise by simply sitting in park and switching to Auto or Fulltime.

It's a faint squeeling noise - similar to the horizontal / fly-back section of older TVs.

Anyone else have this? Super annoying!

Thanks.

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tbully said:

Confirmed. Stuffing a towel up there temporarily has muted it somewhat. This isn't safe to drive with obviously so I just tested it in the garage.

Mind snapping a picture of your job?

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revengejr said:

I just posted this on another thread but just saw this. Here is our problem:
We just leased a 2015 1/2 Tahoe LT. My wife started complaining of a high pitched noise coming from the dash on the left side but I couldn't hear it. We took it back the dealership and they couldn't hear it either, until my wife convinced them to have their receptionist sit in the car and she immediately heard it. The dealership immediately swapped us to an identical new Tahoe since we had just picked up the car less than 48 hours earlier and their service manager said he can not fix something he can not hear. (very accommodating dealer) New truck had no noise...until while playing around with settings, my wife turned the 4wd selector knob from Auto (which was set from the factory) to 4wd. The high pitch noise came back. Now, unless she keeps the knob on 2wd, she hears noise on Auto or 4wd, effectively making our new truck a rear-wheel drive car. I did some testing with a sound meter and tone generator. The sound is somewhere around 15kHz at about 44db, which is loud - if you can hear it. Think a train passing relatively close by but ear-piercing. I apparently can't hear tones above 14,600Hz and when I tested several colleagues using a tone generator, generally everyone over the age of 40 couldn't hear any tones above 14,800Hz, however a few young women in my office could hear tones above 15kHz. A quick Google search verified that in fact this is a normal, previously known fact that young women can hear very high pitched tones older women and most men can not hear. Go figure. Now, we have a brand new Tahoe on a 39 month lease we just got that we can't take out of 2wd since it causes my wife to get a serious headache. Is this the same thing you were hearing? If so, what was the fix? Replacing that part? The idea of wrapping a leased car's parts in foam may not go so well. The dealership says they've never heard of this and want to bring someone from GM in to have at it. It seems to be coming directly from the selector knob or something immediately behind it. Any advice or suggestions would be immensely appreciated! Thanks!

***EDIT
It's also worth mentioning she hears the noise even while going at 2mph or 60mph as long as she is depressing the accelerator. Doesn't matter the speed.

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