Rhythmic thumping/knocking noise under deceleration
 

Hello,

Making a post to ask for advice and document the repairs.

My 2013 Brz with 43,500km (roughly 27000~ miles) developed a noise in what I can only describe as a "rhythmic" thumping/knocking noise dependent on wheel speed, under deceleration, and while in gear.

It ONLY happens while the car is in gear and decelerating from speeds above 70kph (43 mph). The sound DISSAPREARS when the drivetrain is under load (accelerating or maintaining speed) or disengaged from the wheels (clutch pushed in or in neutral). It doesn't make noise when doing U-turns in either direction.

I was almost certain its just the CV joint, hopefully I can just repack it with grease and not have to replace the whole axle.

BUT I jacked up the car and started wiggling the axles with my hands to confirm my suspicions. They seem to have the same amount of movement but one side seems to make more noise than the other. Both sides do also seem to have grease that have leaked out from the boots.

Although what worries me is I also noticed that the connection between the diff and the axle has some movement as seen on the video. I am honestly completely unsure if this is normal because it's the first time I've touched this part of the car.

I tried to take a video of the noise the car makes while driving but I don't think its loud enough to be evident with my phone's mic when I checked the video. You can absolutely feel and hear it in person though.

Here's a short video of me wiggling the axle under the car showing the noise the axle makes and the movement I was talking about.

https://www.youtube.com/watch?v=xh3fdhRebss

The car's diff oil was just changed less than 2,000km ago and has only been to one circuit event since. But prior to that, it is used in circuit, autocross and occasional drifting.

Sorry about the long post, I'm trying to be as descriptive as I can because I couldn't get the noise on video.

I'm currently waiting for new CV boots to arrive so I'll try to repack them then I'll update here.

I'm wondering if the movement in the video is normal? and if there is a larger underlying issue aside from the CV joint? (if the cv joint is actually the issue).

I personally have not killed a CV, nor has any others I have talked with. The left side CV on the diff does have a tendency to cook the grease in the diff side due to the exhaust. It’s a good idea to repack it from time to time with some good high temp grease. I am not too concerned with the movement in your video. It’s hard to tell the noise, it kind of sounds like the retaining clip on the shaft going into the diff to me.