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Sienna 2001 -- dentist-drill like buzzing from back left of car

I have a 2001 Toyota Sienna with 115,000 miles on it. After about 15 minutes of driving, a vibrating buzzing dentist-drill like sound begins to come from the back left of the car (this is also where I put in the gas if that has anything to do with it). I do not know what it sounds like from the outside but its definitely a buzzing sound from the inside. As I increase in RPMs the buzzing sound gets more and more high pitched.

I do not drive this car very much, but about a month ago I was driving down a mountain using the breaks a lot and the buzzing sound started for the first time with a rubber smell. At this point because of the rubber smell, we just thought it was an issue with the breaks and after taking a 20 minute rest, the car drove the rest of the 400 miles or so perfectly fine without any buzzing. I don’t use the car very much because I am in college, but when I do, like I said, after 15 minutes this buzzing starts.

If anyone has any advice about what could be causing this it would be greatly appreciated. Also if anyone knows how much the fix will cost, that will also be greatly appreciated.
Thank you

Could be a problem with the brakes, a wheel bearing, or the fuel pump. Or just something rattling, like the cat heat shield. You’ll need to get a mechanic to do a visual inspection. It might be obvious once the car is on the lift.

Based on my experiences, I believe that your electric fuel pump–which is located in the area from which the sound is emanating–is going to die very soon. It would be better to replace the fuel pump before it fails, in order to avoid the inconvenience of being stranded, and to avoid the extra expense of needing a tow.

However, you should have your mechanic check the pump before deciding whether to replace it. Don’t just replace it based on my distance diagnosis.

Even though the sound seems to have originated right after heavy use of your brakes, I think that this is merely coincidental. And, just for future reference, when driving down a long downgrade, you should downshift the transmission to a lower gear, so that constant use of the brakes is not necessary.

If you continue to use your brakes like that, you will break your brakes.

My first choice would be fuel pump is getting noisy. You might hear more noise when the fuel tank is low. If the noise changes after you fill up the gas tank that makes the fuel pump more likely the source.

Abs brakes and trac control systems do have components that can make noise, so it is possible this is a brake problem. Is the ABS light illuminated on the dash? If you’ve not been changing brake fluid every 3 years then a brake problem is a possible. Not likely, but possible.

What bothers me about the fuel pump diagnosis is the statement by the OP that “As I increase in RPMs the buzzing sound gets more and more high pitched.” I don’t think that the sound of a fuel pump is tied to RPM. If, however, you mean the speed of the vehicle, then I think you have a wheel bearing problem. Do you hear the buzzing while the engine is running, but the car is not in motion? If you do, it is not a wheel bearing. However, if you don’t hear the noise unless you are moving, I’ll bet on the wheel bearing.

“I don’t think that the sound of a fuel pump is tied to RPM.”

I’m going to disagree with you on this point, Triedaq.
While my experience with failing electric fuel pumps is admittedly limited to just my '74 Volvo, I had at least 5 of them fail on that rolling timebomb of a car, and I found that the buzzing sound from my failing fuel pumps did increase in pitch as RPMs increased.

Doesn’t it make sense that, given the need for more fuel at higher RPMs, the fuel pump would be turning faster and thus might make more noise?

I support Triedaq’s opinion that an electrical fuel pump operates at constant speed. A standard fuel pump does not have any speed control. During normal operation, it actually pumps more fuel than an engine can use, the surplus being returned by an overflow line.

Any of the above suggestions might be valid. I might add another possibility – the brake pad wear indicator. Have your car checked out on a lift.

Related question: it’s my understanding that many modern cars have done away with the return line. I think my Compass is one. Does the pump still run at a single speed in this case?