Well I hate to post this, but I've about worn out the search engine here looking for answers... Guess I'll just throw out some facts and thoughts and see if anyone has anything else to offer.
The truck: 2011 DC 4x4 SR5, 7,200 miles, Eibach coils, 5100s at 0, TSB springs. No problems with this set up since March.
Only recent addition: ARB bumper last week - no clue if it's in any way related.
So the past couple of days, I've noticed a steady, low whistling or humming noise. More accurately, it would probably be best described as a harmonic tone of some sort - kinda like you're blowing on an old glass coke bottle. It's not super loud, but it's audible enough that it's bugging my half-deaf ass.
During regular city driving, it starts up around 35-40mph and remains constant up to around 60 or so (my normal top speed on my commute). I took it up to 70 a little while ago, but I think the road noise simply overcame the mystery noise. If I stay at a steady 30 or so, I can get the noise, as well. Either way, the noise remains pretty constant until I get below 30 or so as I'm coming to a stop. There's no noticable vibration associated with this tone.
Now initially, I thought the sound was for sure coming from the front passenger side, but after some poking and prodding today, I'm not so sure.
I've pushed on windows and pulled on doors with no change. This is actually where I changed my mind about where it was coming from - when I'd lean over to the passenger side to tug on the door or push on a window, the sound seemed to migrate to a more ambiguious location somewhere toward the front of the truck.
So ruling some other things out...
- Braking - doesn't change anything
- Speed - doesn't change anything
- Let up on the gas - no change
- Lay in to the gas - no change
- Change gears - no change
- 4h - no change
- I've experienced the cross-wind windshield buzz. This isn't it.
- Windows up, windows down, it's still there
- Haven't done any off-roading aside from a dirt road or two
I thought maybe the wind was playing the jugs with the new ARB bumper, so I taped over some open areas around the signals as well as the open ends of the hoops which protrude to the interior of the bumper. No change.
When installing the ARB, I had to flip up and zip-tie the front fender liners. Dunno if this might be the cause. I haven't messed with them so far.
When I got home a while ago after a little troubleshooting drive, I popped the hood and listened to the engine. It actually sounds like I can hear a very similar tone in the engine at idle up under the engine cover. Maybe something to do with the air box, so I'll look at that.
Things I haven't messed with yet:
- Drivetrain stuff - axles, spindles, control arms, driveshafts, u-joints, etc
- Air intake stuff - air box, filter, etc
If I can't figure it out, I'll take it to the dealer, but for now, I'd like to at least make an attempt to stay as far away from there as I can.
I'm really hoping this doesn't get into bearing/differential territory at my mileage...