Knocking noise on suburban
 

Hey everyone, I have a 1997 gmc suburban 5.7L N/A, has about 80,000 miles, most of which was used for towing a boat or getting construction parts or other heavy loads.
When the car is on the freeway generally 65+ if the car Idles or coasts to a lower speed then it makes this Loud ass knocking/clanking noise, if the brake is engaged then the noise cuts off rather abruptly. I also believe turning might stop the noise(not sure on that one)

I know a good amount about cars, could this be the Flywheel or crankshaft bearing due to high rpms with towing?

any help would be awesome.

I don't know if this is your issue but I know on my 97 tahoe with a 5.7 I had to run at lest mid-grade or premium for spark knock... you might try a few tanks of high octane fuel to see if it changes the condition

a. 4wd?
b. what turns may stop the noise, left or right?
c. noise only on coast or deceleration not on accel? Nor if the brakes are applied?
d. does it sound like its coming from the front or rear or middle of the car?

It is a 4wd not Awd.
I think its both left or right, but not sure.
but yes the noise is only on coast or idling, Accelerating or braking puts it to a stop

it sounds like its coming from the engine compartment but it is very noticeable throughout the whole car.

I will also try the premium gas, thanks

IF its not happening under load its likely not ping or knock so high octane won't help... sounds like you might have a connecting rod coming loose...

I d check the locking hubs in the front. If its that electronic shift on the fly junk one wheel may be locked and the other free-wheeling. And look behind the steering knuckle also. The axle shafts arent the same length in the front so the shorter axle may may have a bad CV joint and or no grease in the boot. Jack it up and take a look.

Aight man, ill do that. thanks for helping

Kinda feared as much, thanks for the advice

If you can drop the oil pan a quick inspection of the connecting rods and caps to the crank is easy enough...
You may want to try a stethoscope or the trusty closet rod dowel to different places on the the engine block to see if you can identify any sounds while the engine is idling.. if something is loose inside the engine it will also make noise at idle it just may be harder to hear....
Its actually pretty cool to "hear" the inside of your engine working...
and I will state the obvious of "Be careful when placing anything on the running engine that is attached to your body"...


FYI harbor freight has them for $8 or less http://www.harborfreight.com/mechani...ope-41966.html

"Be careful when placing anything on the running engine that is attached to your body"... Lol, you just made my day.
but ya your right ill try hearing it when idling
thanks

you laugh but I am almost certain this forum (by no fault of its own) has spawned a Darwin award winner or two....:eek:

DO me a favor bro, and take a minute and actually make a checklist of the problem. I m not sure if its rattling, knocking or tapping. And open the hood and try to isolate the sound. From what you said, I think its a driveline/suspension part. But others say its a lower end engine situation. I m not sure then WHY the noise goes away on braking. I had a situation with a Mercury station wagon that did that rattling sound that went away on braking and when I put it on the lift the hold down bolts on the caliper were loose. Just an idea...and direction to look in.
Engine noises have nothing to do with turning or braking and would perceptively be louder on acceleration or under load. A connecting rod would rattle more as it slapped around the bore under load. But sloppy tie rods, sway bar links, pitman arm/idler arm bushings, and rotted bushings in the control arms can cause clanking especially on poor road conditions. CV joints can cause noise on turns. And broken hub solenoids, loose axle nuts, hold down bolts cause rattling on coast and go away on braking.

hey bro with the 97 suburban. i have a 97 suburban sle 5.7l v8 i had the same knockin noise as you with the same symptoms the other day when i was drivin a trailer full of hay it got louder but only when i stepped on it. today on my way to school i ended up throwing a connecting rod through my oil pan. so if i were you i would get it looked at or look into it yourself but into more detail. also if you blow a rod dont try and start it your just gonna cease the engine then your screwed

New need help and kind of related to topic
 

I have a 96 Chevrolet suburban and I hear knocking when in park reverse drive 3 2 and 1 when I accelerate from a stop light or on a stop a quick knocking noise happens quickly about 2 sec or 3 then normal again I don't know if it's transmission going out , or what ? I have towed twice a trailer holdin atleast 3500lbs after towing it started the noises it has roughly 189,000 miles need help sorry about posting in existing new to this and can't find new thres on this small screen message or reply back need help ASAP thanks for you time