I know there are some scattered threads here and there about something similar!

But I'd prefer this was in the general section where it may get more feedback and traffic. Under light throttle my car exhibits an annoying hum. As soon as I let off of the gas it stops, if I am hard on the gas it is not there. Unfortunately this hum is present at 60mph which is where I spend most of my time. I had the differential oil changed today and it did not change. I recorded some video on my phone and the sound is quite obvious. Please have a listen and let me know what you think!

http://www.youtube.com/watch?feature...&v=G7SGpvciApQ

 

I've listened most carefully to your "hum" and I instinctively went for something in the silencer/muffler area; my close second choice was torque converter lock up clutch noise. Of course, since I've wrestled (successfully with the help of this website) with my own T.C. clutch, I could be prejudiced.
If it's originating in the clutch, it may be that when the box is fairly cold, the noise is not present. So if you get the noise within a minute or so after setting off, it's prob. not that clutch.
The silencer/muffler could have loose baffles, so try restricting each tailpipe slightly with something suitable to see if it makes any difference.
The noise also reminds me of air input noise (like operating the engine without an air cleaner), so look around the air hoses for any subtle leaks; maybe this effect could create an errorcode?
BTW, good idea recording the noise.
Leedsman.

 

No error codes, and it seems to do it even when I just start out. If it were the baffles wouldn't it do the same thing when the car was parked? It only makes this sound at highway speeds. So your issue was your TC? If so was it replaced or how did you fix the noise?

 

The exhaust gas throughput will be different if you just rev. the engine when stationary, the silencer/muffler noise may well not show then. The noise sounded like something "tuned" or resonating. (And of course, silencers and pipes are tuned on purpose for power or economy). Autobox noises were stopped when I had the ATF fluid changed, that was in a 6HP26 ZF.
Try having a passenger with good musical ears who also has good stereo hearing see if he/she can pinpoint the area of the noise. I once had a Peugeot SRD. model that made a noise like bagpipes in the distance around 45mph. This was the way the wind whistled round some suspension parts in front. BTW, have you made any body additions?
Leedsman.

 

Hmm, doesn't happen when stationary, but at highway speeds only.

Apart from Leedsman's suggestions if it is not the diff or gearbox. Maybe a propshaft bearing or driveshaft. Also check wheel bearings.

Had an MB with a centre prop bearing that used to sing like that.

 

it might be the tires

 

I know for sure it's not the tires. I had the exact same set on my Nissan Z with no issues. And there's no reason that the noise would stop completely when I let off of the gas. If it were the tires the noise would continue regardless.