Dear Doctor: I have a 2008 Toyota RAV4 that makes a slight humming sound. As I continue to drive the noise gets louder and when I put the transmission in neutral the noise stays about the same. The technician said that during my next oil change that I should also change the transmission fluid and spark plugs. Any advice on the humming sound?

Dear Denise: The humming sound is usually found under the hood from the fan belt area, air conditioning compressor or fan belt pulley bearing. A humming sound would not be due to spark plugs or transmission fluid. And if you do replace the plugs and transmission fluid, then use the correct plugs and factory Toyota transmission fluid only.

Dear Doctor: With all the improvements in cars, one problem has remained a constant: the corrosion build-up on battery terminals. Aside from a monthly cleaning with a tooth-brush and lots of water, what can be done to stop it? My local mechanic sprayed some sort of blue stuff, but it did not even last three months. Any suggestions?

Dear Steve: Corrosion on the battery terminals is caused from acid fumes leaking out of the battery to the battery post -- usually the positive terminal. You can try any kind of sealant. If your car battery is four years old, then it would be a good idea to replace the battery before there is a major problem.

Dear Doctor: I own a 2009 Nissan Altima. Last summer the dashboard light indicated a tire pressure issue. My dealer replaced a tire pressure sensor for $276. A week later, another sensor had to be replaced. I discussed the problem with the dealer that it was a bad batch of sensors when my car was built and I was reimbursed for the expenses. Now in early 2015, the dashboard is telling me that a third sensor has to be replaced. I'm anticipating an expensive repair bill. Should these items be malfunctioning?

Dear Duke: The average battery life of a tire pressure monitor sensor is five years. Some will go longer while others are shorter. Some manufacturers use a hard metal tire valve stem that owners sometimes break off when trying to put air in the tires, others break the valve stem when trying to remove the internal valve core to let the air out of the tire. We use a universal sensor that runs around $125 with programming.

Dear Doctor: I have changed every brake part on my 1953 MG, except the drums. The vehicle still exhibits brake fade. No one has given me a solution to correct the fade. Is it repairable?

Dear Lee: Brake fad is caused from brakes that overheat, causing the fluid to get very hot and sometimes even boil. For brake fade to occur, the car has to be driven very hard, fast, and with a lot of hard brake use. This occurs mostly on vehicles driven on the track. However, you will need a complete evaluation of the brake system if this car is not driven hard. A stilling brake caliper or wheel cylinder, if equipped, can cause also brake fade.

Dear Doctor: I own a new 2015 Volvo XC70 T6. The AM radio band bleeds through the hands-free Bluetooth system on the recipient end. There is also some bleeding of AM stations over other AM stations. Volvo has done a reboot of system, as well as replaced the IHU and updated software. Nothing has solved the problem. I had two loaner cars that did the same thing so this seems like a widespread issue and it happens with different brand phones. Why?

Dear David: With the continuing evolution of infotainment technology, manufacturers are less concerned about the AM band. The filtering device on the radio is not strong on the AM band, which is causing the problem. Most manufacturers are focused on FM, satellite radio and navigation, not to mention your handheld wireless device.

Dear Doctor: I recently purchased a 2009 Toyota Camry with 4,000 miles on it. It was parked and unmoved in a driveway for about 18 months before I bought it. I replaced all four tires, changed the oil and filter, battery and belts. When moving from a stop or making a turn I hear water sloshing around from the front of the car. I have had the drains all checked and they are all open. What can be causing such a sound and how do I fix it?

Dear Greg: The most common area of water collection is the heater box. The drain is often blocked by debris and a simple drain opening from under the car is all that is needed. The use of an air pressure blow gun and or a piece of wire is all that is needed. There could also be water stuck in the doors and lower trunk area, as well as the spare tire well.

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