1993 Sierra 5.7 K1500 auto rattle/vibration noise FIXED!

[OleGreen93]

Hello everyone, I’m looking for a little help identifying the source of this strange noise my truck is making. Oddly enough I noticed it for the first time after breaking in my new oem style camshaft and lifters. Break-in went well and I noticed the noise when I was done setting the ignition timing. I can really only hear it in the cab. I’ve gotten under the truck and also listened in the engine bay but can’t really pickup on the location of the noise. I really hope it’s nothing mechanical related. It sounds almost like something is vibrating or coming into contact with something else. Noise increases with engine speed and seems to go away for split seconds when I hit bumps on the road. I was thinking of pulling the transmission inspection cover to make sure it’s not coming from there but when I realized I need to drop the exhaust for that I thought I’d check here first. I’ve swapped to another distributor I had to eliminate that. Thank you for any suggestions!

Video of noise driving 0-30 mph:

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[Eveready]

Is it engine speed or speed over the ground that changes the sound? Can't tell much from the video but if it is the "clunk" sort of low pitched sound I hear it might be a motor mount. if it changes when you hit a bump it could be the drive train lifting and settling. Just floating this... others with more experience might have better suggestions. Be sure and update the thread when you figure it out.

 

[OleGreen93]

Is it engine speed or speed over the ground that changes the sound? Can't tell much from the video but if it is the "clunk" sort of low pitched sound I hear it might be a motor mount. if it changes when you hit a bump it could be the drive train lifting and settling. Just floating this... others with more experience might have better suggestions. Be sure and update the thread when you figure it out.

It is engine speed. I can rev the engine in park or neutral and the sound will speed up. Putting it in 4lo or 4hi doesn’t change anything either. Thanks for mentioning motor mounts. I’ll have to check those and the transmission mount. The clunk you hear at about 10 seconds into the video I believe are my keys hitting the steering column on a bump.

 

[Eveready]

If the frequency of the noise changes with engine speed then it may very well be some mechanical component having to do with the engine. What about the water pump? That definitely makes a engine speed dependent noise. Look carefully at belts etc. Maybe the idler pulley. Could maybe be an alternator bearing about to go. The list gets long. Mounts would not make that sort of noise.

 

[OleGreen93]

If the frequency of the noise changes with engine speed then it may very well be some mechanical component having to do with the engine. What about the water pump? That definitely makes a engine speed dependent noise. Look carefully at belts etc. Maybe the idler pulley. Could maybe be an alternator bearing about to go. The list gets long. Mounts would not make that sort of noise.

I did put a new water pump on it while changing out the camshaft/lifters. The noise only appears to be coming from the floor/transmission tunnel area. Maybe its just a coincidence that I noticed it after the cam break-in. I've never heard a noise like this before from a vehicle and it seems to be getting louder and more noticeable the more I drive it. I may end up having to drop the transmission inspection cover to make sure its not a flex plate or loose torque converter bolts.

 

[man-a-fre]

Out of curiosity what brand cam and lifters did you go with and part no.

 

[Chevy-SS]

I watched the vid and couldn't really tell which noise you were referring to.

When confronted with situation like this, I always revert to the "Occam's Razor" principal....... Occam's razor (or Ockham's razor) is a principle from philosophy. Suppose there exist two explanations for an occurrence. In this case the one that requires the smallest number of assumptions is usually correct. Another way of saying it is that the more assumptions you have to make, the more unlikely an explanation.

So, there was no noise until you changed cam. Therefore, the noise is most likely something that occurred as a result of your work. So I would focus primarily on things (which are a lot, unfortunately) that you touched during the cam install.

This same situation happened to me over the weekend when I put new rotors and pads in front of my '03 Silverado. I used ceramic pads and had horrible squealing noises. So I took apart and used grease on back of pads.... no joy. Then I used CRC disc brake quiet, and still no joy, horrible squealing. Then I took apart one more time and slowly looked around and discovered that I had inadvertently bent a dust shield so that it was contacting the rotor. I bent that back to proper position, and noise was all gone.

I suspect if you do thorough and careful inspection of all parts you disturbed, you will likely find something similar in your situation.

Good luck and please post solution when you find it.

 

[OleGreen93]

You guys aren’t going to believe what ended up being the noise I was hearing! Out of desperation I set my phone to record and set it down on the floorboard while I got under the truck while it was running and tried to feel around again for what might be the issue. Got back out and checked the video and couldn’t believe I was able to get the noise to go away. It ended up being the fuel lines were vibrating against the floorboard causing the noise. Chevy-SS was absolutely right about it being something I touched during cam swap. I’m not sure how they got into a position to contact the floors but I put a piece of weatherstripping between the lines and the floor and noise is gone! Thanks guys for the help!

 

[OleGreen93]

Out of curiosity what brand cam and lifters did you go with and part no.

I bought a sealed power KCT274D cam and lifter kit from rockauto

 

[Eveready]

Congrats on chasing it down. What made it confusing was the fact that seemed to depend on engine speed. Stopping on occasional bounces or bumps make sense considering what it turned out to be. Glad it was not some thing that would have been an expensive pain in the butt to fix.