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Discussion Starter · #1 ·
Hi All,

Ive noticed this strange occurrence in my crosstrek. I have a 2021 premium model with the 6 speed manual. Currently has 5,400 miles on the odometer. Whenever I am going highway speed 55+ MPH I notice a howling noise from the back whenever I let off the gas pedal. Only lasts for the first 2 seconds off the gas then goes away. Super weird. Not a constant noise and doesn’t happen at lower speeds. What could this be? Roof rails? Rear diff? Doesn’t sound mechanic. Almost sounds like some kind of interference.
 

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Check this out:

There is a harmonic damper on the rear crossmember. Ours look a little bit different than the one in that thread.
Motor vehicle Automotive design Automotive tire Automotive exterior Auto part


Maybe yours is missing?
 

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The noise is probably rear diff "hoo" howl from gear lash. I noticed it coasting at about 60mph. I had my 2021 rear diff replaced and noise came back after a couple thousand miles. Recently, a TSB has been issued on the problem, suggesting 75w90 fluid rather than the thinner manual trans fluid(I thought the car came with 75w90). I had put Liqui Moly 75w90 in the first diff and it did not stop noise. I'm thinking trying 75w140 to see if it helps.
 

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The noise is probably rear diff "hoo" howl from gear lash. I noticed it coasting at about 60mph. I had my 2021 rear diff replaced and noise came back after a couple thousand miles. Recently, a TSB has been issued on the problem, suggesting 75w90 fluid rather than the thinner manual trans fluid(I thought the car came with 75w90). I had put Liqui Moly 75w90 in the first diff and it did not stop noise. I'm thinking trying 75w140 to see if it helps.
You're right, only it was the CVT fluid that was thinner. The TSB is for the R152 diff aka the VA-1 type (CVT). The MT has a different rear diff and already had 75w90. It still wouldn't hurt to change it.
 

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Discussion Starter · #6 ·
The noise is probably rear diff "hoo" howl from gear lash. I noticed it coasting at about 60mph. I had my 2021 rear diff replaced and noise came back after a couple thousand miles. Recently, a TSB has been issued on the problem, suggesting 75w90 fluid rather than the thinner manual trans fluid(I thought the car came with 75w90). I had put Liqui Moly 75w90 in the first diff and it did not stop noise. I'm thinking trying 75w140 to see if it helps.
interesting. I initially thought this could be my problem as well. I brought my car in around 6,500k miles for its first oil change and after that i don't notice this noise anymore. It did it for a tiny bit after i left the dealer but I dont hear it at all anymore.
 

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It's not loud and hits at 60-63 mph only while coasting. If you coast from 65 down to 55, you will hear it begin at 63 and quiet down below 60.
What gear are you in when it happens? Does it happen in 5th as well as 6th? How about Neutral?
 

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Actually, more like a mourning dove, "hoo," than a wolf howl. Problem had also been noted on WRX forum years ago and SOA specified a bolt on damper to stop the resonant noise. My Crosstrek already has a damper of sorts bolted to the rear subframe.

I haven't tried coasting at 60 mph in 1st, 2nd or 3rd, but noise is audible in 4th, 5th, 6th gear, neutral, or with clutch depressed. Not sure about CVT trans. Regardless, it's a rear diff noise, so not gear dependent, and only when coasting and no torque on gears between 63 and 59 on my car. May be slightly different on any car. It's a gear lash noise.

There is a TSB on it and SOA recommends replacing rear diff fluid with 75w90 gear lube to quiet the noise. Even though the factory manual specifies 75w90 for the rear diff, "apparently" the factory may have filled the rear diff with the thinner gear lube used in the manual transmission for mpg like (0w20 oil), and they think 75w90 will be enough viscosity to cushion the gears and stop the lash noise. Perhaps they are thinking non-synth lube, which would be thicker than synth.

When my issue first occurred at just over 1000 miles, I tried 75w90 Liqui-Moly synth on a hunch, but there was no difference. Dealer replaced the diff and was quiet at first, but noise came back at about 1500 miles on new diff. When I get around to it, I'm going to throw a quart of 75w140 synth in to see if it's thick enough to cushion the slack and stop the noise. If that won't solve it, I will live with it before I put in non-synth lube.

I have a hunch that I put too many highway miles on car when in break-in period despite varying speed.

Rev hang with 6MT is more annoying.
 

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Actually, more like a mourning dove, "hoo," than a wolf howl. Problem had also been noted on WRX forum years ago and SOA specified a bolt on damper to stop the resonant noise. My Crosstrek already has a damper of sorts bolted to the rear subframe.

I haven't tried coasting at 60 mph in 1st, 2nd or 3rd, but noise is audible in 4th, 5th, 6th gear, neutral, or with clutch depressed. Not sure about CVT trans. Regardless, it's a rear diff noise, so not gear dependent, and only when coasting and no torque on gears between 63 and 59 on my car. May be slightly different on any car. It's a gear lash noise.

There is a TSB on it and SOA recommends replacing rear diff fluid with 75w90 gear lube to quiet the noise. Even though the factory manual specifies 75w90 for the rear diff, "apparently" the factory may have filled the rear diff with the thinner gear lube used in the manual transmission for mpg like (0w20 oil), and they think 75w90 will be enough viscosity to cushion the gears and stop the lash noise. Perhaps they are thinking non-synth lube, which would be thicker than synth.

When my issue first occurred at just over 1000 miles, I tried 75w90 Liqui-Moly synth on a hunch, but there was no difference. Dealer replaced the diff and was quiet at first, but noise came back at about 1500 miles on new diff. When I get around to it, I'm going to throw a quart of 75w140 synth in to see if it's thick enough to cushion the slack and stop the noise. If that won't solve it, I will live with it before I put in non-synth lube.

I have a hunch that I put too many highway miles on car when in break-in period despite varying speed.

Rev hang with 6MT is more annoying.
Definitely get a tactrix and subaruedit to get rid of that revhang. I had that done and now it's almost like I can't shift fast enough as the revs drop rightr away. Feels like a car from the 90s again.
 

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Actually, more like a mourning dove, "hoo," than a wolf howl. Problem had also been noted on WRX forum years ago and SOA specified a bolt on damper to stop the resonant noise. My Crosstrek already has a damper of sorts bolted to the rear subframe.

I haven't tried coasting at 60 mph in 1st, 2nd or 3rd, but noise is audible in 4th, 5th, 6th gear, neutral, or with clutch depressed. Not sure about CVT trans. Regardless, it's a rear diff noise, so not gear dependent, and only when coasting and no torque on gears between 63 and 59 on my car. May be slightly different on any car. It's a gear lash noise.

There is a TSB on it and SOA recommends replacing rear diff fluid with 75w90 gear lube to quiet the noise. Even though the factory manual specifies 75w90 for the rear diff, "apparently" the factory may have filled the rear diff with the thinner gear lube used in the manual transmission for mpg like (0w20 oil), and they think 75w90 will be enough viscosity to cushion the gears and stop the lash noise. Perhaps they are thinking non-synth lube, which would be thicker than synth.

When my issue first occurred at just over 1000 miles, I tried 75w90 Liqui-Moly synth on a hunch, but there was no difference. Dealer replaced the diff and was quiet at first, but noise came back at about 1500 miles on new diff. When I get around to it, I'm going to throw a quart of 75w140 synth in to see if it's thick enough to cushion the slack and stop the noise. If that won't solve it, I will live with it before I put in non-synth lube.

I have a hunch that I put too many highway miles on car when in break-in period despite varying speed.

Rev hang with 6MT is more annoying.
"I have a hunch that I put too many highway miles on car when in break-in period despite varying speed."

I believe this is the same issue I'm having, too many miles at highway speeds with a new car. I bought the car about 150 miles away from home.


"When my issue first occurred at just over 1000 miles, I tried 75w90 Liqui-Moly synth on a hunch, but there was no difference. Dealer replaced the diff and was quiet at first, but noise came back at about 1500 miles on new diff. When I get around to it, I'm going to throw a quart of 75w140 synth in to see if it's thick enough to cushion the slack and stop the noise. If that won't solve it"
I would love to know the results of this if you do try the 140. I haven't given up on getting Subaru to replace my rear diff. but if this works I may try it myself if my persistence doesn't pay off.
 

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Haven't put in 75w140 yet. Living with Hoo noise. Doesn't bother me as much now that I know what it is. Read a post from a WRX tuner/tech who puts 75w140 in the cars he works on. Did not refer to the gear lash noise in the post, though. I just figured, it's worth a try and will eventually do put it in.
 
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