noise question - So i took my 09 HD2500 LTZ to the dealer today because it has a whine that develops around 35mph and fades out at around 45-50 mph. ...

So i took my 09 HD2500 LTZ to the dealer today because it has a whine that develops around 35mph and fades out at around 45-50 mph. they had it all day and said they took everything apart and came to the conclusion it was the wind? they said it was because i have an aftermarket grill and bug deflector on it. the noise just started (less then 32k on truck) i have had the aftermarket parts on it for a couple years. It sounds like a bearing in the transmission to me, something I'm sure they don't want to deal with? i even took the service writer on a ride and he said it sounded like something in the front? it's not tires, surface condition shows no change. they said they covered the grill with plastic and drove it and the sound went away?? i may try this myself but find it hard to believe that something that wasn't there when i installed it would all of a sudden be the cause. If any of you have any ideas or suggestions it would be greatly appreciated. Thanks!
Millertime

WELCOME to the site!

I was going to suggest removing the grill and bug guard as a possible test. Also, I have heard of bug guards making strange wind noises.

If not, you still have a lot of miles left on the powertrain warranty.

I might try that next weekend, i still have the oem grill, but the bug shield uses an adhesive backed foam and would ruin it if i took it off. but I'm not really convinced it will make much difference since the sound started over a year or so since items were installed? Thanks for the support!
Millertime

I had a similar noies in my wifes Malibu... It turned out to be a wheel bearing going bad. I was covered Under the Power Train warranty.

I had a bug deflector on my 2004 avalanche that caused wind noise too, it was removed.

I'm thinking i should figure out a way to get a sound bite for everyone to hear. i drove to the coast yesterday, and i am almost positive it it is a rotating whine sound and not a wind vibration. i guess the fact that all the after market stuff was in place well over a year, before the sound makes me think dealer is on crack...thanks for the replies!
MT