What's the Buzz

I have a 2005 Dodge Ram 1500. It’s got about 120,000 miles. 4WD. Manual transmission. When I get it going about 40 MPH, there is an obnoxious buzz. It sounds and acts like a tire problem, but I have rotated the four tires and spare all around and it doesn’t go away. I changed out all the pads and rotors and it didn’t go away. The front right bearing was a little loose, so I changed that out. It didn’t go away. I’m pretty sure it is coming from the front because I can kind of feel it in the steering wheel. What else can I do to locate this buzz?

"Sounds and acts like a tire problem"
Can you clarify? do you feel it in the steering wheel and or the calves of your legs? My first guess is a heat shield, but that would not act like a tire problem

Sounds like something might be resonating in a particular frequency range. Have you gotten under the truck and checked for all the usual suspects, like a loose heat shield or exhaust hanger?

It is a kind of a buzzing, vibration type of thing as if I had big knobby tires. Pitch varies with vehicle speed. It doesn’t matter what the engine is doing or whether the truck is in gear. I feel it in the steering wheel, but not in the calves.

I’d expect a heat shield to rattle if you rev the engine. It wouldn’t be proportional to the vehicle speed would it? I guess it’s possible something is resonating. I will definitely take a close look at that.

If the noise changes in intensity (not frequency) as you saw the steering wheel back and fourth, it’s probably the left front wheel bearing.

Sawing the steering wheel doesn’t have any effect on the noise.

Does it happen wherever you’re driving that speed, or have you noticed it only on certain roads? I ask because there are freeways in places with grooved concrete surfaces (to limit hydroplaning) and the grooves sometimes interact with tires at particular speeds. It can be quite loud and felt as a judder in the steering.

That is pretty much what it sounds like, but the sound happens everywhere. I can start to feel a little something driving around the neighborhood at 30 MPH.

Even though you rotated the tires I would still suspect them if they all have the same tread pattern. Most tires produce some noise, especially as they rack up the miles.

Edit: Just want to add I wouldn’t rule out a wheel bearing (left front) since it is proportional to vehicle speed.

I checked the exhaust system and that seems to not be the problem.

So I took it back to the shop. My mechanic took it for a test drive and put a stethescope on it, but he couldn’t really make a definitive diagnosis. He suspected a defective part and changed the right front bearing again, but that did not help. It could be the left front bearing. It could be a bearing in the differential. He can’t isolate the problem.

Where do I go from here? Drive it until something catches on fire? Change the left bearing and cross my fingers? Start over with another shop? Maybe a transmission place might be more familiar with the bearings in the differential? I dunno.