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narrowing down a mysterious thunk


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19 replies to this topic

#1 grossgary

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Posted 30 March 2012 - 09:24 AM

our daily driver 03 OBSedan H6 has a noise i cant find on the front passenger side.

happens every time and only at 50 mph and above and only when you let off accelerator. its a metallic rap, rap rap sound that follows our out of balance/alignment tires.

almost certainly not the axle for various reasons. cant get anything to move or make the noise grabbing and shaking by hand.

it sounds like something is hitting the dash.

bought it with trans blown and already removed and he had loosened some odd bolts, control arms, etc. ill check all those a third time.

#2 Rooster2

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Posted 30 March 2012 - 09:38 AM

Bad "top hat" strut bearing on top of a front strut??

If so, would also make noise when driving over bumpy pavement.

Edited by Rooster2, 30 March 2012 - 09:39 AM.
added more info


#3 1 Lucky Texan

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Posted 30 March 2012 - 09:40 AM

any strut work done? maybe the mount for the strut has a busted stud or something.

You might look at the anti-sway bar and its mounts too, but that seems like it would be too low for your noise.

edit: DOH, beat by minutes again while composing/spell checking lol!

#4 ivans imports

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Posted 30 March 2012 - 09:57 AM

Check the trans strut brace and trans mounts the go bad alot and high tourque moter hard on mounts

#5 Ricearu

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Posted 30 March 2012 - 12:10 PM

when my wife's car is on the highway and in "tc lock up" and I decel, the trans hits the tunnel because it had totally locked torque bind and broke the trans mount. Does it also if I give it too much gas in reverse. thunk thunk thunk. I guess the U-joint makes it not hit sometimes.

#6 nipper

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Posted 31 March 2012 - 10:58 AM

our daily driver 03 OBSedan H6 has a noise i cant find on the front passenger side.

happens every time and only at 50 mph and above and only when you let off accelerator. its a metallic rap, rap rap sound that follows our out of balance/alignment tires.

almost certainly not the axle for various reasons. cant get anything to move or make the noise grabbing and shaking by hand.

it sounds like something is hitting the dash.

bought it with trans blown and already removed and he had loosened some odd bolts, control arms, etc. ill check all those a third time.


What happens if you pop it into neutral and let it coast?

How many miles

#7 grossgary

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Posted 31 March 2012 - 12:18 PM

150,000 miles, no strut work done that i know of. i just got it last summer so i don't know much history of the vehicle except i installed a new transmission in it.

ah ha - trans mounts, i think you're probably on to something. the mount seemed fine but i recall something happening...like one of the bolt holes was stripped and i meant to get to it later, i wonder if i have a missing bolt in one of the trans mounts? i'll check that first.

i don't think it ever does it in neutral because it only does it when it's under load.

#8 grossgary

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Posted 13 April 2012 - 08:43 PM

no change - it's still there. never does it in neutral...sort of suggests CV's but those don't appear bad in any other way and seem like OEM?

ah ha - trans mounts, i think you're probably on to something. the mount seemed fine but i recall something happening...like one of the bolt holes

it was missing two bolts in the trans mount due to stripped out holes...i chased the threads and installed all the bolts - no change.

#9 1 Lucky Texan

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Posted 13 April 2012 - 10:25 PM

swap axles left-to-right.

#10 markjw

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Posted 14 April 2012 - 01:49 AM

I just tracked down a rattle that Mostly happened during deceleration. But, at low speeds. Turned out to be the inner brake pad vibrating against the brake caliper piston, but only when the engine would vibrate a certain way. A little grease on the back of the pad fixed the problem completely.

A quick tap on the brakes when I heard the noise made it stop instantly.

#11 grossgary

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Posted 14 April 2012 - 07:33 AM

A quick tap on the brakes when I heard the noise made it stop instantly.

that is a strange one. it sounds more "inward" than that, but who knows.

i need a brake friend to sit over there while i'm driving and contort around to see if that can help narrow down where it's coming from. or i'll let them drive and do it.

the axle swap is probably a good recommendation. i think i saw a little grease coming out of one axle, but it's nowhere near ripped all the way or anything...

#12 1 Lucky Texan

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Posted 14 April 2012 - 09:06 AM

have you had the wheel off? maybe you have a cracked wheel stud?

#13 mwatt

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Posted 16 April 2012 - 02:40 PM

can you determine if the "rap rap rap" happens once with every revolution of a wheel/axle ? My wife's 98 Outback did exactly that when a CV joint was failing.....on deceleration a "thunk thunk thunk" once with every revolution of the axle...and of course the thunking slowed as the vehicle speed slowed. And when that CV joint failed, there were no grease leaks. Thunk, thunk, thunk; rap rap rap, bang, bang bang.....however you wish to term it....it was once with every revolution of the axle. Also made the steering wheel shake violently until vehicle speed dropped below about 45.

Edited by mwatt, 16 April 2012 - 02:45 PM.


#14 grossgary

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Posted 16 April 2012 - 03:34 PM

i have had the wheel off - i can't visually see anything, nothing seems loose or shaky.

i have now noticed that it will ocassionally "thunk" or "rattle" when i hit a bump. oddly it won't do it on large bumps every time...it's like it has to hit just right.

i'll pull the wheel and look at brakes and axles.

#15 CNY_Dave

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Posted 16 April 2012 - 03:58 PM

Could even be clapped-out sway links/bushings.

#16 brus brother

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Posted 16 April 2012 - 07:10 PM

loose heat shield? or is sound louder?
pound on exhaust, see if there is any sound,

#17 Caboobaroo

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Posted 17 April 2012 - 07:06 PM

Gary, have you checked the caliper for looseness? It seems to be pretty common that the slides get a bit loose because the grease solidifies in the caliper bracket, which can cause the caliper to bounce more then usual. Once the wheel is yarded off, grab ahold of the caliper and see if it moves and might be the cause of the noise. Since you're in there, also check the condition of the pads to help eliminate variables.

#18 grossgary

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Posted 09 October 2012 - 03:36 PM

Could even be clapped-out sway links/bushings.

Ding Ding, this was it.

It got worse and I was just under it the other day. I can easily, without much effort at all slide the sway bar from side to side inside it's bushings with one hand. I suspect that's probably the issue?

Will try some new bushings and see what happens.

#19 CNY_Dave

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Posted 09 October 2012 - 06:08 PM

If it can move not sideways but up/down in the bushings, maybe, but usually a sway-bar clink is from the end links.

They can look fine but be bad and noisy, but more often they look bad when they are bad. Depends on the style.

Posted Image


Posted Image

#20 grossgary

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Posted 09 October 2012 - 11:06 PM

oh really, sideways is okay?

it does not move up and down at all.

i'll check endlinks and compare it to my wagon. never seen a bad endlink or replaced one before so not familiar with those very much.




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