fire24resque

Anyone have or can diagnose this problem?

When my truck is idling warm, every 20-30 seconds there will be this dull "thunk" that comes from somewhere on the truck. You can hear it and if you are totally still, feel it. It sounds like someone lightly punched the side of your truck through a pillow. I've gotten out before and crawled under it and heard it, but I have NO clue where it's coming from. It's loud enough you can hear it outside and inside of the truck, but it's not THAT loud. It almost sounds like something switching over, like for say the transfer case from 2wd to 4 but I never push anything! Anyone?

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2001 Silverado 4x4 - 4.8 V8 BFG 265/75/R16 A/Ts

K&N FIPK - Ravin Muffler 3.5" Duals
4-Headlight Conversion Kit - Billet Grille
LED Line of Fire Bar - 90 Watt Nova Strobe Pack
Sirius Satellite Radio - Pioneer Head Unit
Pioneer 6 Disc CD Changer - 2.5% Limo Tint

Check Out Pictures and More Here
http://www.cardomain.com/ride/2131569/1

Rammer500

I'd bet thet is the AC compressor cycling. The compressor will run when you have selected the defrost setting.

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fire24resque

This happens with the defroster/fan etc.. all off. Nothing is running but the truck itself.

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2001 Silverado 4x4 - 4.8 V8 BFG 265/75/R16 A/Ts

K&N FIPK - Ravin Muffler 3.5" Duals
4-Headlight Conversion Kit - Billet Grille
LED Line of Fire Bar - 90 Watt Nova Strobe Pack
Sirius Satellite Radio - Pioneer Head Unit
Pioneer 6 Disc CD Changer - 2.5% Limo Tint

Check Out Pictures and More Here
http://www.cardomain.com/ride/2131569/1

mikethehammer

i have that same noise, don't know what the hell it is

85lolo

get out and watch the compressor even when off I think the cycle, may be wrong though

OGG

I think my truck does the same thing. On most newer cars the A/C compressor cycles periodically to keep everything lubricated internally.

Mork

Yes the AC compressor will cycle on/off even without the AC turned on. I believe it does this as a sort of de-humidifier to reduce cab humidity and as so fogging of the windshield.

jumpingjack66

you described it as a thunk. I would take that description and suspect that ypou mayn be hearing the fuel tank expanding and the side of it thunking in or out . Perhaps pressure from recycling fuel build and then is release on a cycle? If you had said a tick or somthing then i would suspect somthing turning on or off but a thunk is something moving.

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2000 Silverado Victory Red, standard cab, short bed, short wheelbase, 4X4, 4.8L, 5 speed, 4:10 locking rear diff, K&n FIPK, Ryno lined all the way over bed rail, heavy half suspension,factory skid plates,Fog lights, BFG 285/75/16 A/T's, dashmat, Stealth Radar.
lots of special options some installed by me!

1980 Suzuki GS1100E Super fast

masapell

My compressor also thunks, but I have never really checked to see if it does that when the ac is off.

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2000 Silverado Ext.Cab, 5.3L, Pewter, True Flow Foam Filter, Airaid Intake, Flo-Pro Performance muffler, Hayden 679 Rapid Cool Transmission Cooler, Hidden Hitch

green silverado

I've experienced something similar... exactly the way you've described... not only in my truck but in my car... I was told this is normal... go figure.