Odd Sporadic Sound - 2000 Subaru Legacy Wagon

subaru

#1

90k and auto transmission. Sound comes from the right front - specifically at or under right side fire wall. Sounds like a train horn at a distance or lifting metal lid of large dumpster. Happens about 3 out of every 4 driving events at no particular time. Happens only once during a driving event (key on/key off). Always at 15 to 25 mph. Lasts 3 to 4 seconds. Same smooth uniform frequency from start to end. On a few occasions, the sound is immediately followed by a much quieter version lasting about 2 seconds. Not related to braking, accelerating, putting in gear, shift points, reverse or turning. Person in right front passenger seat with feet on slanted part of floorboard will feel strong vibration in right foot. No other odd car behavior when sound occurs. Started 6 weeks ago. No recent repair, maintenance or damage events to consider as cause. Just got back from 1,000 mile trip and it ran like a top. Felt front wheels every 200m and they stayed cool. But the odd sound occurred nearly every time I drove it. Car is serviced and inspected every 2,500 miles. New transmission and timing belt one year ago. Brakes and tires have less than 10k. Both in good shape at last service.

This is a first for me. I don’t have a mechanic’s ability or knowledge, but I’ve owned 16 vehicles over 50 years. Help please.


#2

Wow…thats a good one. One thing to remember is vibrations travel.

It happens with key off? You mean with car off and parked it happens?


#3

Not when the car is off. It happens each time I use the car between key on and key off. I was trying to make clear it happens just once during any one use of the vehicle. Sorry for the confusion.


#4

A couple of things that come to my mind are your blend door & fresh air vent. I don’t know the Subaru system but - for example - if your fresh air door is vacuum actuated and squeaky it very well might do this every time you start the car. I suppose it might also do it even if it isn’t vacuum actuated. This is the kind of thing that a lot of people don’t often mess with - I almost always have mine set to fresh air. Fiddle with your air controls unless you have already.


#5

Took it in July 24 and your idea is one of two the mechanics hit on. The other is a malfunctioning AC accumulator tank. The AC works fine so they want me to play with all those controls now and then and keep notes for awhile. They did not charge me.
Just as I got ready to leave a new mechanic came on shift. He asked if it sounded like a loud tuba. That was the sound I was searching for. He said he had seen it in one Subaru seven years ago. Said they fixed both the tank and worked on vent controls to make it stop. Thanks for all comments.