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very loud knock while accelerating increases with speed, 06 grand prix

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stumpee1

New member
while driving my 06 grand prix started knocking loudly (no ping, loud knock). the knock increases in speed as I accelerate (like a card in bicycle tire) its kind of like I can feel it in the accelerator pedal as well. it only happens while driving is fine giving gas while parked. Does anyone have any ideas? my catalytic converter is in rough shape as well if that helps? connected problem?
ty for any possible assistance
 
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Yea was kinda thinkin that, but am hoping its just a stuck lifter or a busted flywheel.

stumpee1- check out videos on YouTube of 3800 rod knock and see if that's the sound you're hearing. If so, motor swap time.
 
I was just editing thread to say it only happens while driving is fine giving gas while parked. ok I will look into rod knock. tyvm for replies guys
 
I've been having a similiar issue. Ticking noise only during acceleration while the car is moving. No noise when the car is in park/neutral and given gas. I think it's an exhaust leak but I'm too lazy to figure it out lol.
 


With odd sounds your trying to figure out, it's always best to post a video clip if possible. Makes it a guessing game otherwise.
 
I do understand that, but I have no access to video, sorry. I am leaning towards axel, cv joint or something since revving engine in park is fine
 
the question is if it varies witht he cars speed or engine speed. is noise present while rolling on highway and shifted into neutral. noise present under acceleration in reverse? is there a sharp knock during a quick goose of the throttle in N/R/D. does noise change with wheel steering angle?
all oem parts with 500,000miles?
catalytic converter in rough shape? buddy that could mean so many damned things.... is it rattling in the housing? is it plugged or just a cat efficiency code?

since you have given us very little info ill assume that like most its not had any major parts replaced and is at approx 100-150k miles.

quite possibly bbad/sagged mounts have led to the exhaust being able to tap against the swaybar, or allowed the flex to break and your hearing an exhaust leak (made worse by plugged cat), or the cat is actually plugged and the engine is under enough strain your hearing/feeling an intake side backfire.

if wheel speed related, it could be a loose/missing caliper bolt, loose lug nuts, slipped/seperated tire belt and a bad steering linkage.

since everyone has an old phone...charge it up, ziptie it in differnt areas of the engine bay while recording, find loudest recording, look for problem in that area
 
wow tyvm for the reply. I just went out to verify and the knocking/ vibrating is there in reverse gas or no, the noise does not change with steering it is still the same. I would say it definitely has to do with movement. It definitely gets louder and quicker with speed.
About the catalytic converter the car got VERY LOUD a while ago, I was thinking muffler but noticed the welds were breaking on the seams of the catalytic converter. But it has driven fine since that. I know next to nothing about cars and am somewhat financially challenged lol.
ty again is a great help
 
probably a broken flex , a plugged cat or a partially plugged cat tends to stress the stainless bellows till it cracks., it drops down and can hit the swaybar and bounce against it.

put two hose clamps downstream of the flex section with the worms on either side near the bolts, lift it back onto the manifold, use mechanics wire to secure around the worms to around the DP/manifold flange bolts to hold it in place.

it'll still make noise but its a bandaid
 


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