Cyclic (Sine Wave) Hum...

[Soulkeeper]

So we took the truck on the first big trip these past 10 days. With Covid and all, and my short work distance, I rarely get 70+

Halfway from Lima, OH to Cincinnati I begin to hear a cyclic sine wave pattern hum. It starts soft, then grows loud (at times very) and then dissipates, and repeats barely 3-5 seconds between end and restart. It happens at or near 72+, sometimes hitting the gas will stop it for a short while, other times taking foot off gas will, but it returns.

It almost sounds like that reverb hum you get behind the engine when accelerating before the gear shifts. Hopefully this makes enough sense to someone.

I had the joy of hearing this for 10 day through the state of Tenn, until our return last night.

I did a bit of Googling, and saw someone else with a similar issue. The thread (elsewhere) had no resolution, but one person said to use the Gear Limit and shift it out of automatic to 8 to see if the sound disappeared. It did not. They then said try 7. At 7 it stops. At 72 the engine of course picks up sound as the truck is pushing the gear limit, but the cyclic hum vanishes.

I cannot believe this is normal, but I'm not sure what it might be and how serious it might be. Looking for advice. It is however not a pleasant driving experience.

 

[WW2]

sounds like ANC system...some have reported needing software update to correct...

 

[borden72]

Where does the sound come from inside the cab? I'm hearing a similar sound from the driver rear in the roof. Mine happens to occur when the drivers vented seat is set to low. I need to take it in to have them check it out.

 

[Soulkeeper]

I hear it loudest by my left ear, but my wife can clearly hear it in the passenger. It "sounds" like it is reverberating the entire left side, but I cannot hear it with the windows down (albeit doing 72+ MPH) to tell if its outside as well.

 

[Soulkeeper]

Well my local dealer asked to have me drop it off next Monday, and keep it all week. They checked recalls and I am good, but he did confirm that it is not a normal thing. I mentioned both MDS and ANC, also pointed out the Gear Level trick, and he seemed intrigued.

However, I am still open for suggestions and (if anyone has had the same issue) wisdom from all of you.

@borden72 I am 99.9% sure I don't have vented seats. Didn't know that was a thing.

 

[Buz]

Mine has something very similar at 37-40 mph with all windows up. It's a cyclic drone from the back seat area. It's not the ANC or MDS. I've disabled both and it still does it.

 

[borden72]

Well my local dealer asked to have me drop it off next Monday, and keep it all week. They checked recalls and I am good, but he did confirm that it is not a normal thing. I mentioned both MDS and ANC, also pointed out the Gear Level trick, and he seemed intrigued.

However, I am still open for suggestions and (if anyone has had the same issue) wisdom from all of you.

@borden72 I am 99.9% sure I don't have vented seats. Didn't know that was a thing.

My 2019 Laramie has vented seats but the noise I hear isn't speed related other than changing the level on the vented seat (low, med or hi).

 

[Richard320]

https://5thgenrams.com/community/threads/the-droning-is-gone.14871/

And it's still gone.

 

[Soulkeeper]

https://5thgenrams.com/community/threads/the-droning-is-gone.14871/

And it's still gone.

I am printing this, thank you. They are taking my truck in next Monday, so I will bring this. Thank you!

 

[mikeru82]

@borden72 I am 99.9% sure I don't have vented seats. Didn't know that was a thing.

You don't have vented seats. It's not available in the Big Horn trim level. Need to step up to a Laramie, Longhorn, or Limited to get them.

 

[Soulkeeper]

https://5thgenrams.com/community/threads/the-droning-is-gone.14871/

And it's still gone.

@Richard320 and to everyone who gave advice, thank you.

I had taken your post advice, loaded the truck with gear (~200 in cab) and played around with various weights in bed, and was able to reproduce the issue time after time at 72.

Called, explained issue, made an appointment and dropped it off yesterday.

Picked up my truck this afternoon, and they applied not only TSB 08-056-19, but (I wasn't given the TSB info) an update for PCM and TCM that they felt were related and might help improve things over all.

It is now whisper quiet!