So ice been tackling this for awhile and I'm stumped. When going over bumps I'll feel a grinding or rattle through the floor boards and gas and brake pedals. I've replaced sway bar bushings, sway bar end links and bushing, and replaced the intermediate steering shaft. And I still have the noise! Ball joins are tight! Can anyone help me!?

 

Anyone?

 

I have a constant vibration from the driver's side floor board. I feel it in the pedals as well.
My engine also shakes like hell. Does your engine shake in the engine bay? I'd check that out first. I've given up on fixing it. I've replaced everything, like you've said. It's power train related (engine, tranny specifically, not drive shaft, etc).

Oh, does your steering wheel shake too?

 

Nope, my steering is actually fine and my engine is fine too. Mine on rattle over bumps. But your issue kinda sounds like a u joint. I had a duramax and my u joint was shot and making exactly rattles just like yours. Though with your motor moving that might be a engine mount.

 

Some customers may comment on a snap or popping-type noise coming from the front of the vehicle. This condition is most apparent during hard left or right turns at low speeds. Going over bumps while turning may also aid in producing this noise.
<a id="d75369e50">CorrectionRemove the bolt-in front crossmember and add washers using the procedure listed below.
Important: DO NOT slot the mounting holes on the crossmember as stated in previous bulletins. Slotting the holes has been found to be less effective and, in some cases, causes the noise condition to be more prevalent.

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in SI.
2. Remove the mounting nuts, bolts and the front crossmember from the vehicle.
3. Clean all the undercoating off the crossmember in the area of the mounting holes.
4. Reinstall the crossmember with the bolts and nuts. On the driver and passenger side, add washer P/N 11509592 (C/K models) or P/N 15567836 (H2), or equivalent hardened washer (see dimensions below), at each bolt head and nut location.
   Tighten
   Tighten the bolts to 120 Y (89 lb ft).
5. Apply an even coat of Anti-Corrosion Coating, P/N 12346501 (in Canada, 10952414), or equivalent, to the crossmember where removed. Overlap the original coating in order to provide an effective corrosion protection.

Inside Diameter
Outside Diameter
Thickness
14 mm (0.551 in)
35 mm (1.38 in)
3 mm (0.118 in)

Inside Diameter
Outside Diameter
Thickness
14 mm (0.551 in)
24 mm (0.945 in)
3 mm (0.118 in)
<a id="d75369e234">Parts InformationPart Number
Description
Qty
11509592
(C/K Models)
Washer
8
15567836
(H2)
Washer
8

 

Tranny or transfer case mounts good? Also check clearance with the cat guard, some have found them bent against the tranny or cat, causing vibrations and rattles.