Dear Tom and Ray:

I am a member of the military living in Minot, N.D. None of the mechanics in Minot, including the dealership, seem to know what is making my 2003 Toyota Tundra 4x4 truck make a loud vibrating noise. It isn't the alignment or tires, and it doesn't appear to be the bearings. The vibrations only begin around 22 mph, and then get increasingly louder/stronger up to about 45 mph, when they go away.

The vibrations are there whether I am accelerating, coasting (even in neutral) or braking. To make things crazier, the vibrations go away ENTIRELY when I switch the truck into four-wheel drive. Some days (rarely) the vibrations don't show up at all. Is it harmonics, poor engineering, a problem with the differential or drive shaft? The vibrations appear to be located under the front driver's side of the car -- right underneath the driver's seat, near the wheel. Any ideas? Thanks.

-- Kyle

TOM: Well, if you're confident that the tires are well-balanced, the next thing I'd have someone check is the drive shaft. Maybe you hit something and bent it, or maybe there's a worn-out or seized universal joint in there. That's easy to check.

RAY: When they tell you the drive shaft is fine (because it's rare for a drive shaft problem to "not show up at all" some days), then you'll want to grab your wallet and hold on to it tightly and dearly.

TOM: Because then the problem is more likely in the transmission or transfer case. The fact that it goes away when you engage four-wheel drive suggests that something is worn out near the output shaft of the transmission. The dealer or perhaps a transmission specialist is the best person to investigate that.

RAY: But be aware that it may be difficult to diagnose with a high degree of certainty, and that whatever they propose to fix probably will be very expensive. So I'd be reluctant to authorize a big repair unless you have a lot of confidence that your mechanic has absolutely identified the source of the problem.

TOM: Alternatively, you could just keep driving and wait until whatever is vibrating eventually falls off. Then you could jump out of the car, go over to the side of the road, pick it up, take a cab to the nearest parts store and say, "Give me one of these." Good luck, Kyle.