HVAC blower noise, is this normal or am I crazy?

[C6Joe1957]

I'm wondering if any owners of higher mileage Y51 M's notice a low "buzzing" sound coming from the front passenger side behind the dash and if so, is this normal?

I acquired my '12 M56 last spring and after getting used to it and with no stereo sounds, noticed a low buzzing noise related to the speed of the blower fan. Mostly when the fan speed is set at about 30%-70%. So I decided to get a replacement thinking that the blower's motor bearings were wearing out on this previously owned SoCal car with 100K plus miles.

I bought a brand new blower unit, installed it and it still makes the exact same buzzing noise.

[Ilya]

Nope, can't say I've heard that...I have a 2011. Doubt you're crazy, but something is likely afoot.

[VStar650CL]

It's possible there's some stray foam or debris caught in the airway somewhere that's vibrating. That may not be easy to locate. If your blower is a brush type, it's also possible you're hearing HF from the PWM signal to the blower resistor. I personally can't hear it, but I have met customers with very sensitive ears who claimed they could.

[C6Joe1957]

It's possible there's some stray foam or debris caught in the airway somewhere that's vibrating. That may not be easy to locate. If your blower is a brush type, it's also possible you're hearing HF from the PWM signal to the blower resistor. I personally can't hear it, but I have met customers with very sensitive ears who claimed they could.

Could that mean that there's an issue with the resistor and if you think so, could you explain? I can't comprehend why the resistor could cause the noise with my lack of knowledge with electrical/electronics.

When I installed the new blower I heard the exact same sound as before. So I put the original back in and heard the same noise, tone and all.

[VStar650CL]

Could that mean that there's an issue with the resistor and if you think so, could you explain? I can't comprehend why the resistor could cause the noise with my lack of knowledge with electrical/electronics.

No, it would just mean you can hear something most people can't hear, like some folks can hear the tiny buzz from the triac in a ceiling fan but most can't. I'd pull the blower again and the cabin filter as well, give all the seams in the HVAC box that you can reach a careful tactile inspection. If there's anything loose, remove it and see if the noise stops.

[JCesar]

I have the same sound that you have. if i turn the music off then i can hear it. it sounds like a bad bearing just like you said. I been meaning to get a blower and most likely will replace it right after winter. did you get a factory one?

[jd3rdcoast]

I get similar noise from driver side during HVAC operation on my ‘13 M56S. Been there since purchased in ‘15 w/35K miles. @75K now. Stops when turn off HVAC.

[EdBwoy]

For those affected by the sound, do you think it can be captured on video/audio?
If so, I think it would be helpful if somebody would record a video of this issue so we can see how it starts, advances with blower speed, and what it takes to stop it.

[C6Joe1957]

For those affected by the sound, do you think it can be captured on video/audio?
If so, I think it would be helpful if somebody would record a video of this issue so we can see how it starts, advances with blower speed, and what it takes to stop it.

Hopefully this loaded. https://youtu.be/TLw2xyh7Mcc

[VStar650CL]

Sounds like something whistling inside the HVAC box. I'd still check it for foam protrusions, etc, but if it's deep inside then you may never find it without yanking and disassembling the box.

[EdBwoy]

Yep, I was able to watch your video Joe. It sounds like the car is about to take off.

It is not normal, and what I would do to isolate the noise is to take the blower back out and run it while carefully holding it in my hands (still connected to the wire). Run it at varying speeds in different positions - upright, sideways, upside-down, etc

[C6Joe1957]

Sounds like something whistling inside the HVAC box. I'd still check it for foam protrusions, etc, but if it's deep inside then you may never find it without yanking and disassembling the box.

I should've done this yesterday but didn't have the time.

Yep, I was able to watch your video Joe. It sounds like the car is about to take off.It is not normal, and what I would do to isolate the noise is to take the blower back out and run it while carefully holding it in my hands (still connected to the wire). Run it at varying speeds in different positions - upright, sideways, upside-down, etc

I'm going to perform both these suggestions today along with getting rid of the somewhat annoying weather alert announcement. I'll try to get pic's and a video of my results and post up later.

Thank you Guys!

[VStar650CL]

You're most welcome. Keep in mind, because it's high frequency, it takes only a vanishingly small amount of energy to create an audible noise. Any little protrusion can conceivably cause it. The last time I managed to cure one like it, the culprit turned out to be a pine needle that made it past both the cabin filter and squirrel cage, lodging itself in the mix door channel where it stuck out in the breeze and drove the owner crazy.

[C6Joe1957]

Finally getting back with results of removing the blower unit, cleaning out the chamber which had collected some dirty residue and trying to file and sand the blower fan's outer ring after observing mars which I thought might be rubbing with the inside wall of the chamber.

From the top:


From underneath:



Outer rub marks:


Tried filing first:


Then tried 60-grit paper:



Unfortunately there wasn't much of a improvement as you can hear from the very beginning and at the end of this video. https://youtu.be/bWXF5ClvoEk

So I guess I'll have to live with it.

[VStar650CL]

That's definitely motor noise, and doing it with the motor loose excludes problems in the airway. Maybe you just got a bum replacement, but it's possible there's electrical jitter coming out of the blower resistor if that's going south. You might want to try a different resistor before you give up.