odd noise in 240

Could be a universal joint. They make some weird noises.

bf

I'd guess a wheel bearing is going bad. You can test it by carefully doing lane change-type sideways turns while it's making the noise: if it gets louder going one way and softer the other, it's a wheel bearing. If, on the other hand, it gets worse when accelerating or decelerating, and lessens while going a steady speed, the driveshaft carrier bearing is the likely culprit. Universal joints are more likely to vibrate than make noise, at least at first.

Could it be tires?

Tires would probably make the same noise at the same speed, regardless of of throttle. You seem to have a load-dependent noise. Frankly, the description puzzles me.

Ok, after thinking it over I came up with two likely possibilities:

1. The differential is low on oil, and/or the gears in it are worn.
2. (More likely) the trailing arm bushings are worn, allowing the rear end to move forward and back slightly under load. When it moves back, the carrier bearing complains. Our 240 actually had this happen; I wouldn't have described the noise as you did, but I can see why you might.

Is the heat on? On both my 1990 244 and my wife's 1993 245, there's a whistle or whine in the heating system, which generally only occurs at highway speeds. If I move the thermostat lever a bit it temporarily goes away.

Thanks for the replies and the time and thought put into them.

I apologize for the odd description I gave. I'm having an issue relating it because I've never come across it before. The more I listen to it the more it seems to sound like some kind of pressure leak. To describe it another way, which is still rather vague, is to liken it to a tea kettle. Once I've driven 50 mph or higher for a couple miles I hear a build up to a steady whining noise. If I release the throttle the whine slowly diminishes. Like taking a tea kettle that is whistling off the heat. To describe the actual noise the best I can do is compare it to the engine noise (the hum) you might hear through poorly wired radio speakers, only clearer and higher pitched. I know it seems juvenile but it sounds just like a tea kettle going off in my car.

I thought about the radio, turned it off. Considered the air system, turned off the fan and closed the diaphragm for the outside air. I closed all the windows. Still get the noise.

I keep coming back to it sounding like some kind of pressure leak. The problem with that is I can find no sign of any kind of leak much less one that only happens at high speeds.

As for bearings, the sound is steady taking curves left or right, if that tells you anything. The rest of what you've described is beyond my knowledge so I can't confirm or discount it. Looks like I have some reading up to do.

Perhaps one of the vacuum hoses to the heater and related ducting is loose or has a hole in it.

You can probably rule out wheel bearings. That leaves you with a driveshaft carrier bearing complaining (they can do that for years without failing), or, another possibility, an alternator bearing that is just starting to go. We also had that happen, and the noise did *sort of* fit your description. Or it's something else entirely. ;-(

Try this test. Pull the fuse (3#) and see if it goes away. Put the button controls on recirculate (Far right button only) to keep outside air from getting in and turning the fan.

Even though the fan switch is off it still spins at a low speed.

All my heater fan bearing failures in three 245's started with that whine.

My 90 currently has a small exhaust gasket leak between the manifold and pipe leading to the cat that sounds the same. Only it goes away once everything is hot.

Duane

That is exactly the sound our cars make. When it's happening, try moving the slider for the heater.