A Noisy Honda Has Maggie Stumped

Dear Car Talk:

In hot weather, I occasionally hear a very loud horn-like sound when I drive at 65 mph or higher. The noise appears to be on the passenger side, toward the front of the car. The local Honda dealer and a local mechanic have checked belts, windows, sunroof and the hood latch. It seems to happen only when I am driving on a curve, and it will stop if I slow to less than 65 mph. I need your help. Thanks.

-- Maggie

Well, since you've had several mechanics look at this, I'm going to make two assumptions. Well, three, actually.

Assumption One is that the mechanics have heard the noise. Assumption Two is that once they've heard the noise, they've ruled out something dangerous, like a failing wheel bearing, and they're convinced it's more likely a wind noise -- which explains the stuff they've checked so far. And Assumption Three is that, since two shops have already been all over the car, I have no chance of figuring it out. 

Back in the old days when a customer had a problem like this, we'd strap my brother to the hood of the car and then go for a drive and try to reproduce the sound. When we got back to the shop, we'd take the leaves out of his mouth, and ask him which direction the noise was coming from. 

There's a more modern-day version of that: We have a tool at the garage that has a bunch of small, wireless microphones that attach with hook-and-loop tape straps, suction cups or magnets. With that tool, we can attach a bunch of sensors to various parts of the car and then drive the car, tuning in to one mic at a time. That allows us to home in on the exact location of the sound. That in itself doesn't solve the problem, but it at least narrows it down and gives us a fighting chance.

My first guess on something like this -- although it's just a guess -- would be a bad windshield seal. As the speed of the car increases, the body flexes more. And when you make a turn at 65 mph, the windshield opening may be flexing just enough to move the windshield gasket or seal and create a wind noise.

So here's what I'd do: First, I'd ask your dealer to confirm that he's ruled out anything dangerous, like a wheel bearing. Then I'd look for a shop that has one of the listening devices Imentioned earlier. Like NSA Motors. 

And then try out some theories. Put a couple of microphones around the perimeter of the windshield, and see if the noise is very loud near one of them. Or you can do it yourself by duct-taping your iPhone on there ... as long as you have the dropped-phone replacement coverage. Good luck, Maggie.