Help me identify this knocking sound?
Thread Starter
Drifting
Joined: Dec 2000
Posts: 1,785
Likes: 91
From: Leander TX
Help me identify this knocking sound?
Sorry for the video orientation but I think you'll hear it pretty good in this video - https://www.youtube.com/watch?v=n-IX...ature=youtu.be
I'm stumped on what is causing this. I just got the car back together after a major overhaul (Miniram swap, exhaust (catback) change, new rack and pinion, new AC (everything), new power steering pump and hoses, new brakes (calipers, pads, rotors, lines, etc), Smog pump delete bracket, as well as a few other things. Engine is a ZZ4 with about 10K miles on it. Trans has 60K+ miles on the rebuild.
What I have done to find the source:
- Thinking maybe a rod knock. Does not increase with RPM and in fact goes away. I changed the oil and no signs of metal (no metallic dust at all). Oil pressure is solid.
- Thinking maybe Transmission. Car shifts through all gears good. Changed trans fluid and filter. I didn't see much at all in the fluid and less clutch media than I thought I would. Fluid had 10K miles on it and was still pretty clean.
- Thinking maybe something in the accessories. Noticed the AC bracket was cracked so I replaced it. No change in the sound. Nothing stands out. Sound really sounds like it is coming from under the passenger foot well area.
I put the car up on my drive on lift and didn't notice anything but I could have overlooked something.
Any thoughts on what the sound could be from?
I'm stumped on what is causing this. I just got the car back together after a major overhaul (Miniram swap, exhaust (catback) change, new rack and pinion, new AC (everything), new power steering pump and hoses, new brakes (calipers, pads, rotors, lines, etc), Smog pump delete bracket, as well as a few other things. Engine is a ZZ4 with about 10K miles on it. Trans has 60K+ miles on the rebuild.
What I have done to find the source:
- Thinking maybe a rod knock. Does not increase with RPM and in fact goes away. I changed the oil and no signs of metal (no metallic dust at all). Oil pressure is solid.
- Thinking maybe Transmission. Car shifts through all gears good. Changed trans fluid and filter. I didn't see much at all in the fluid and less clutch media than I thought I would. Fluid had 10K miles on it and was still pretty clean.
- Thinking maybe something in the accessories. Noticed the AC bracket was cracked so I replaced it. No change in the sound. Nothing stands out. Sound really sounds like it is coming from under the passenger foot well area.
I put the car up on my drive on lift and didn't notice anything but I could have overlooked something.
Any thoughts on what the sound could be from?
Safety Car
Joined: May 2001
Posts: 4,759
Likes: 1,647
From: Fairfax Virginia
Maybe something broke loose inside your catalytic converter or exhaust system? It sounded loudest towards the center of the vehicle. Maybe "as the pressure builds up in the exhaust system the broken part stays in one position and rattles around primarily at idle?
It sounds "heavy and clunky" where ever it is, rattling around in there. It sounds like a part that is shaking the worst at idle and smooths out when you rev the engine.
When my Ford 390 rods started making noise they made a real "solid" metallic knock that never missed a beat and only became a bit quieter when decelerating.
That does not sound like a bottom end problem to my old/bad ears, then again but I am no expert on what they "would" sound like. I would get it on a lift quickly so you can do a more careful inspection and identify the source.
Best regards,
Chris
It sounds "heavy and clunky" where ever it is, rattling around in there. It sounds like a part that is shaking the worst at idle and smooths out when you rev the engine.
When my Ford 390 rods started making noise they made a real "solid" metallic knock that never missed a beat and only became a bit quieter when decelerating.
That does not sound like a bottom end problem to my old/bad ears, then again but I am no expert on what they "would" sound like. I would get it on a lift quickly so you can do a more careful inspection and identify the source.
Best regards,
Chris
Last edited by ctmccloskey; Sep 23, 2019 at 04:09 PM.
Melting Slicks
Joined: May 2014
Posts: 2,895
Likes: 592
From: New Port Richey FL
Have you tried unbolting Torque Converter and sliding it back to take Transmission out of the Picture?
I have also seen Catalytic Converters Break if Bad enough it could make you feel like bottom end is coming apart.
I have also seen Catalytic Converters Break if Bad enough it could make you feel like bottom end is coming apart.
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
Just had nasty sounding slapping noise the other day, it turned out to be the torque converter bolts were lose. May want to check them. Stick a wrench on them even if they look tight.
Melting Slicks
Joined: May 2014
Posts: 2,895
Likes: 592
From: New Port Richey FL
Given the Fact the that the car is 30 plus and probably had some really stuck Bolts on the Cat. and required some serious impact gun action, or even some rough Handling when Motor & Trans was upgraded. I more suspect the Cat. Converter.
Thread Starter
Drifting
Joined: Dec 2000
Posts: 1,785
Likes: 91
From: Leander TX
Appreciate the feedback. The cat has less than 500 miles on it but my wife just reminded me that she didn't remember hearing any noise until I bottomed out on a driveway recently. Forgot about that timing as it hit hard enough to move the rear y and mufflers even thought it was a real slow speed impact (maybe 5 mph). I redid all the but only visually looked over the front exhaust components.
Guess I'll pull it off and see what's up. If anyone has any other thoughts keep them coming as I'm making a list.
Guess I'll pull it off and see what's up. If anyone has any other thoughts keep them coming as I'm making a list.
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Thread Starter
Drifting
Joined: Dec 2000
Posts: 1,785
Likes: 91
From: Leander TX
Figured I'd come back to this as I finally got a chance to put it on the lift and let it run for a while. Confirmed, it's the cat. Ordered a new one and will hopefully be up and running again. Thanks for the tips!
