93 Impreza - Mystery Popping Sound in Dash After Decelerating - Any ideas?

[tinfever]

For at least a few months I have had this popping sound coming from what sounds like is inside the dash after decelerating from highway speeds. I am hoping that someone has heard this before or can help me pinpoint cause. I'd like to fix it if possible or at least know that something critical is failing or going to leave me stranded.

 

This is a 1993 Subaru Impreza Wagon/Hatchback and has an EJ18 1.8L SOHC engine with manual transmission, AWD, and no ABS.

This sound only occurs after the car as warmed up (it is silent when cold), after driving at 50+ mph for at least a few minutes, and then decelerating and driving around slower.

 

Here is a video where you can hear the noise I am talking about: 

This video has the driving around cut out. This is after I have driven probably 5 miles at 55 mph and then slowed down into a subdivision. You will notice that it starts making a popping noise which sounds like it is somewhere in the middle of the dash. This is noticeable after getting off the highway but becomes even more noticeable once I slow down further from 35 mph to 20 mph. 

During the course of this video, I move the camera around between the drivers side and passenger side under the dash, and the on top of the dash.

This noise is noticeably louder if there is a bigger difference in speed. Example: 70 mph freeway to an almost stop off an exit. 

This sound does not exist when the car is completely still. Or if it does, there are only one or two pops and then it stops.

You will notice that the noise is not rhythmic and fairly random. I do not believe this is a problem with a engine rotating part, otherwise the sound would exist when revving the car in neutral; which it does not.

This video was taken over a month ago and the noise has become louder/more severe when it occurs.

This sound started somewhere around the time after I replaced timing belt (and other regular replacement parts normally done at this time), water pump, thermostat, flushed the cooling system and added brand new coolant. This may or may not be related.

 

Has anyone heard anything like this before? Any hypothesis? Is my car dying a slow painful death?

 

Thanks in advance!

[Fairtax4me]

Probably one of the inner axle joints getting ready to break. The one on the passenger side tends to fail more often since it sits above the catalytic converter and gets exposed to more heat. The boot splits and flings all the grease out then the inner parts get run dry and eventually wear out.

 

Should be able to see it from above by looking down behind the air intake tube.

[tinfever]

That's interesting. That never would have occurred to me. How would it cause a noise that is not rhythmic though? I would think that it's a rotating part so any noise should be very repetitive and extremely speed dependent. Also, why would it only make noise after the car is hot?

 

I will go take a good look that those.

 

I'll also mention that I have a pretty severe clunking/rattling noise on the front passenger side when hitting any kind of bump. I need to get in there and see what's go on. I'm doing my struts anyway at some point and I'm sure something else needs replacing in there.

[tinfever]

I checked on what I think you were talking about. The inner axle CV joints. They look find to my uneducated eye but here are some pictures:

 

Passenger Side Inner CV Joint

 

 

 

Driver's Side Inner CV Joint

 

 

Hopefully these pictures aren't showing up absolutely massive.

 

What do you think? Do you still suspect an issue there? Any other ideas?

[Fairtax4me]

It does seem a bit odd that the noise doesn't seem to speed up as the vehicle speed increases.  

 

Really just too difficult to say from listening over the internet. Probably going to have to take that to a mechanic, or have a friend who knows cars ride along and help you narrow it down. 

[Bushwick]

I'd get under the car (safety 1st and when it's cooled off) and start grabbing everything and see if something is loose, broken, etc. 

 

Exhaust can make odd knocking noises. When I 1st got my Saab, the edge of the cat (where top cover meets bottom cover, there is a flange on most cats) was bumping the unibody tunnel and it made the noise more so at highway speeds. I carefully bent that flange lip with vice grips and the sound stopped.

 

Other areas that can make noise is a failed bushing somewhere (exhaust hangers included) on anything from sway bar mounts, to trans crossmember support, etc. 

 

I'd look at every bushing and see if one is blown out and the bushing sleeve is resting on metal, inspect the trans area carefully, inspect the dog bone link at the top of the trans back near the fire wall (mine has a rather simple one at top center of trans right by the firewall), check motor mounts, etc. Look for anything hanging that appears out of place.

Edited March 1, 2016 by Bushwick