Strange Knocking Noise From Transmission?

[Acanaceous]

As title says, there is a strange knocking or rattling noise coming from my transmission.

Background: Shifting into second in my 2016 BRZ makes a strange whirring noise when shifting under higher rpms (~4k+ RPM). This strange noise continued for a while as I figured it was just some wear noise despite the vehicle only having about 16k miles at first notice of the noise. I showed this noise to a more advanced friend and he stated it sounds like a faulty synchro.

Just last week as I was travelling down a 55 MPH highway, this noise became very evident. Strangely enough, the noise was only present when in 2nd, 4th, or 6th gear. 1st, 3rd, and 5th made no noise. I drove the vehicle the other day and attempted to replicate the noise with no success. The vehicle drove in a standard manner.

Below I have linked a google Drive file that is a 50 second clip of the noise. Alongside the noise, there is a rattling can; however, I am sure you all will be able to tell the difference as it is quite apparent. Any suggestions as to what this could be would be very appreciated. I am taking the vehicle tomorrow to the dealership for examination.

https://drive.google.com/open?id=1NB...uDWfWCjEK02Gld

[humfrz]

Welcome to our forum, Acanaceous , -

Do you have any power mods?

Have you slammed the transmission lately?

I have no idea of what may be ailing your transmission.

However, I will ring up our MT expert @Ultramaroon for you, to see if he has any ideas.

I think it's a good plan to have the shop take a look at it, check the fluid level and maybe even change the transmission oil.


humfrz

[beltax90]

It;s the next gen coming to say hello

[Ultramaroon]

Do you feel it in the gearshift lever? Does it correspond to engine braking? Coasting? Good recording.

[Acanaceous]

@humfrz I've got a Jackson Racing supercharger on but otherwise bolt-ons such as a UEL header and catback. The noise discussed in the background information and not the posted video was around far before the supercharger was attached. I haven't banged on it no but your suggestion sounds about right.

@Ultramaroon Yeah sorry, it was a spur of the moment recording since I had already developed a suspicion regarding the transmission's integrity and had to have it recorded. The video posted exhibits a funky noise as a result of me depressing my clutch as I am coasting off of a first gear acceleration at a point where one would ordinarily shift into second. Here, I drop the shifter into 2nd, 4th, and 6th while never releasing the clutch. While in position of 2nd, 4th, and 6th gear, the noise emits. At a stop light, I check all of the positions in neutral using the same method described and nothing seems to happen.

Thank you all for the replies.

[Ultramaroon]

No, I mean that it's a good recording. Clear.


Humfrz oversells me. I'm stumped. Please let us know what you find.

[Mr.ac]

Are you on the oem clutch or have an ACT clutch?
What kind of tranny fluid do you have in it?

Take this with a grain of salt, but the last time I heard the same crunchy notchy sounds was when one of the clutch springs was about to come out. But that's a far off chance.

As for the tranny fluid you could try out changing it for another brand, or something other than oem.

[Spuds]

Only thing I can think of is a problem with the shifter-gearbox alignment. Possibly some mounting point is giving up, though that would be quite a strange issue.

This seems to be affecting three different collars but only on one side of the 1-2 and 3-4 collars (6th is it's own apparently). That is leading me to believe something has caused the gearbox or shifter to be misaligned in the longitudinal axis.

There's a good YouTube video here describing the internals

[Acanaceous]

@Mr.ac OEM clutch, the supercharger has been on for 4k miles and I was intending on replacing the clutch with an ACT. It has the same transmission fluid from factory.

@Spuds Longitudinal alignment was discussed by a friend of mine as his "final theory" so your theory would align with his. Thanks for the video link.

Thanks for the replies everyone, I'll be bringing the vehicle by the Subaru dealership today and will update the forum accordingly.

[Acanaceous]

Update: So it seem Occam's razor prevails once again in that the apparent cause of the noise was a dislodged bolt in the drive shaft causing it to knock against its surroundings. I drove the vehicle hard on the way back home and couldn't get a concerning noise to emit so I think it's fine for now. The shift into second seems considerably better now so I consider the issue at hand resolved for the time being.

Thank you all for your thoughts.

[Decep]

yikes. glad you caught that.