Hearing your car make unusual or unpleasant noises is always a cause for concern, and the same goes for when you suspect noises are coming from your car's automatic gearbox. An automatic transmission may be less complicated to operate than a manual one, but that doesn't make it any less complicated mechanically, and a variety of problems can cause your gearbox to make unexpected noise.
One of the most alarming noises your gearbox can make is a sudden, high pitched whine. If your gearbox does start to whine unexpectedly, the ideal course of action is to take your vehicle to a professional mechanic or specialised gearbox repair service, who will be equipped with all the tools and know how to accurately diagnose and fix problems with gearbox whining. However, in many cases you can diagnose a gearbox problem yourself by noting the distinctive sound that it makes, so pay close attention to when the whining occurs while driving your vehicle.
Steady whining when driving
A whine that occurs and remains steady when driving often indicates damage or wear to the planetary gear set; this component is unique to automatic transmissions, and consists of a small centre gear surrounded by a number of smaller gear cogs that work in tandem. This device ensures that automatic gear shifting is smooth and efficient, and failure of the planetary gear set can cause catastrophic damage to a gearbox, especially if failure occurs while driving. As such, whining when driving should be considered a serious issue, and you should take your vehicle to a professional gearbox repair service as soon as possible.
Uneven whining when driving
If the whining is uneven and alters pitch as you drive, however, your problem is likely to be rather different. This modulating whining is often caused by a faulty torque converter, the device which provides your car's transmission fluid with the pressure required for it to assist in gear shifting. The bearings of these devices are often vulnerable to wear and tear, and a good way to confirm that your whining if caused by a worn torque converter is simply to place your gearbox in neutral; if the torque converter is the culprit, the whining will cease.
If your torque converter has failed, mechanical assistance is not an urgent requirement, but you should still have the problem fixed as soon as possible. Besides the constant whine getting rather annoying, a gearbox running with no torque converter can be much stiffer when changing gears, causing your gears to suffer increased wear and tear.
Whining in reverse gear
This problem is often caused by a clogged filter in your gearbox's transmission fluid reservoir, and is caused by air rushing through the clogged filter at high pressures as the flow of liquid is altered. This issue is not a huge problem in and of itself, and cleaning or switching out your transmission fluid filters will generally solve the issue. However, a filter clogged with shards of metal can indicate more dangerous transmission damage, and necessitates a speedy visit to a mechanic. Silt, grit, and other forms of organic detritus should also be a cause for concern, as they may indicate a leak in your gearbox's fluid lines.