Dear Tom and Ray:

I'm from Huntsville, Ala., the home of the Space and Rocket Center and Werner von Braun, the famous German rocket scientist (knowing this tidbit now qualifies you as an historian of Huntsville!). Anyway, I have a 1991 Mazda 2600i pickup with 63,000 miles. Recently, it was brutally cold here, maybe 6 degrees F. I left the vehicle parked outside, not in my garage like I usually do. The next day, I started the truck and drove it to work. I noticed that at speeds over 40 mph, there was a sound I had never heard before. The sound it made was the same sound you hear when you drive over one of those grated steel bridges -- a rather loud humming noise. The sound is only noticeable at speeds over 40 mph. There is no difference in how the truck starts or drives, except for that awful humming noise. Did something happen to it the night I left it out in the cold? -- Kim

Ray: First of all, Kim, my only knowledge of the famous rocket scientist Werner von Braun comes from satirist Tom Lehrer, who wrote this tongue-in-cheek musical tribute to Dr. von Braun, and the way his groundbreaking (literally) research was ultimately used by Germany in World War II: "Some say our attitude, Should be one of gratitude, Like the widows and orphans in old London Town, Who owe their large pensions to Werner von Braun."

Tom: Werner von Braun aside, Kim, the problem with your truck probably didn't happen on any single night, but it may be related to your recent cold spell.

Ray: It could be a number of things, but I'll give you two possibilities. If the grease in the axle bearings got congealed in the cold weather and wasn't "loose" enough to do its job, one of the balls in the ball bearings could have gotten spalled (roughed up in one spot). Once a ball gets spalled, it can cause the bearing to make a humming or growling noise from then on, and that noise is often most noticeable and most constant at higher speeds.

Tom: So have your mechanic take out the axles and spin the bearings to see if one feels rough. If it does, rejoice, Kim. That's a relatively inexpensive thing to fix. An axle bearing can be replaced for about $100.

Ray: If it's not an axle bearing, something may have happened inside your differential, which is much, much more expensive to fix. So if I were you, I'd definitely go to my favorite house of worship tomorrow and light a candle for an axle bearing. Good luck, Kim.

Stop the madness! You can stop driving like a knucklehead, and you'll help your car in the process. Learn how your driving habits can harm your car in Tom and Ray's pamphlet "Ten Ways You May Be Ruining Your Car Without Even Knowing It!" To order, send (check or money order) to Ruin, P.O. Box 536475, Orlando, FL 32853-6475. You can also order online.

© 1998 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

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