Low Feq. Hum or rumble between 50~70 mph

[kingsnakes2LT]

OK so I took my car (2010 V6 2LT Auto6) to the dealer last fall and asked the Service Manager to ride with me in the car while I described the Low Freq. Hum/Rumble sound I hear between 50~70 mph. The sound gets louder with speed but the frequency or tone does not change and the freq. or tone does not change as you change road surfaces. That is how I determined it was not Tire noise.

So anyway, the SM stated back last fall that he heard the noise but did not know what the noise was, or where it could be coming from.

Then this week I take the car back to the dealer for an oil change, the belt/pulley squeal, and ask them to investigate the low freq. hum/rumble again.

Well the SM claims there is a problem with my front tires and orders new tires under warranty. He then asks me to take him a ride in the car again before they put on the new tires. During the ride he says he can not hear the low freq. hum/rumble noise now and doesn't have any ideas what I could be hearing.
So he asks me what I think it is. I tell him I think it is either a problem with the drive shaft alignment/balance and the noise is reverb when the drive shaft reaches a certain RPM, or it is muffler drone.

At any rate I want the Dealership/Service Manager to deterime what the noise is from and fix it if possible. I told him if it is muffler drone, I can live with the noise, but I want to know for sure what is the cause. I still have the stock exhaust.

I have had this low freq. hum/rumble since I first took delivery of the car as far as I can remember. Now it's time to get rid of this noise or determine what is the cause.

Currently they are going to replace the front tires, replace the belt, and check the alignment of the pulleys to address the squeal noise (Car was built 9-09 before they changed the belt material).
They still haven't decided what they are going to do about the Low Freq. hum/rumble at 50~70 mph.
I'm suppose to pick the car up on Monday, so I'll see then what they have to say about the hum/rummble low freq. noise.

Sorry for the Long post.
I've had this problem / noise since 9-09.
If anyone has any ideas/simular noise, please comment.

Thanks!

[The Stig]

Now I'm not an expert with autos, but after reading your post it sounds to me like AFM. I'm a little hesitant in saying its AFM because I do not know if AFM kicks in when cruising at highway speeds.

[kingsnakes2LT]

Originally Posted by stieger

Now I'm not an expert with autos, but after reading your post it sounds to me like AFM. I'm a little hesitant in saying its AFM because I do not know if AFM kicks in when cruising at highway speeds.

Please explain what is AFM and would AFM cause a Low Freq. hum or rumble?
Thanks!

[The Stig]

AFM stands for Automatic Fuel Management system. When it activates it shuts off power to part of the engine and you're only running on 4 cylinders. Thus conserving fuel.

When its active it sounds like a low vibration/humming. So based on your description thats the conclusion I came to.

[kingsnakes2LT]

Originally Posted by stieger

AFM stands for Automatic Fuel Management system. When it activates it shuts off power to part of the engine and you're only running on 4 cylinders. Thus conserving fuel.

When its active it sounds like a low vibration/humming. So based on your description thats the conclusion I came to.

Hey, thanks for your comments.
The Service Manager also suggested it could be that (AFM) (sorry I never heard it refered to as AFM before) and showed me a TSB about the change in exhaust note when the AFM kicks in, however the TSB showed the effected engines and my engine was not included.
I have the 3.6L V6 which does not have AFM because it is Direct Injected. The TSB only listed a 3.9L V6 and the V8s.
Thanks!
Any other ideas/comments?

[The Stig]

Hmmmm I don't know then. Could it just be drone?

[kingsnakes2LT]

Originally Posted by stieger

Hmmmm I don't know then. Could it just be drone?

Ya, I told the SM I think it could be exhaust drone, but I want them to determine what it IS and tell me.
I don't like to guess when it comes to unusual noises/sounds.

[JSC81]

I had a similiar sound normally 65-70. It was found to be something in the tranny resonating so they replaced the tranny. I believe there is a TSB for it now but says something along the lines of we are still investigating it dont replace the transmission.