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What could cause this noise/pulsing in the floor boards?!

2610 Views 3 Replies 3 Participants Last post by  CanX
OK..I have a 2004 Xterra, 4WD non S/C. This is driving me crazy.

When I drive, I get an intermittent/random pulsing/popping noise/vibration in the floor board. I feel it pretty noticeable where my left foot rests under the ebrake, and maybe a bit more faint on the right foot. It doesn't seem to be directly related to wheel speed, but it is hard to determine the root cause since it isn't consistent and doesn't seem to be influenced by wheel speed, transmission gear, engine RPM, etc. It really is bizarre to me. It is not a consistent pattern, but can almost sound like a faint sound of popcorn popping (maybe 4-5 clicks/pops/pulses and it stops for a bit). Speeding up had no impact...letting off the gas has no impact. It does NOT sound like a very mechanical/suspension is more subtle pulsing in the floor board. The noise and pulse has no impact on the driving of the doesn't lose power, slow down, brake from ABS, or happen with suspension cycling.

Here is what I have done:

At first, I was thinking maybe a wheel bearing was "sticking" or not running smoothly at all times. I repacked them and it still made the noise. I then replaced both bearings and repacked with fresh grease/repacking tool, and it still makes the noise. I have inspected all brake components and cleaned all left over dirt from the pads/calipers and rotors. I made sure there were no rocks stuck in the tire treads. The tire spins very smooth with no bearing play.

I completely removed the 4WD hubs thinking maybe they were getting stuck and trying to engage the front Lokka or backspinning the drive shaft. Drove around the block, and the noise was still there. I got my wife to drive slowly and I verified the front CV axles were not spinning (granted it wasn't making a noise driving this slow).

I took the truck to a gravel road and cycled the transfer case and 4WD was working great.

All steering links are rock solid (grassroots center link, good tie rod ends, gusseted idler/pitman arms etc).

Literally, the ONLY clue I have is that it won't make any noise driving slowly (25 MPH or less in my neighborhood).

I think I have ruled out a bearing/hub issue. The transfer case and front driveshaft run right under the drivers seat, so maybe the transfer case is doing something funny, but it cycles through 2hi/4hi/N/4lo smoothly and without issue.

The driver's side catalytic converter and exhaust pipe is right under the pedal area. Maybe one engine bank is having a slight misfire causing a pulsing through the CAT? I have no CEL though...but did scan and find the P0327 knock sensor code. Maybe the 2nd cat is breaking down and causing a noise (that one wouldn't trigger a CEL, as it is down stream from the sensors).

I did get my brother to test drive it and I could barely hear it from the passenger seat, so I think it is more of a feeling than a noise...but he did confirm that I am not losing my mind and that there is something going over there.

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Nice idea...I don't have a stock bumper anymore, so that bracket doesn't exist.

I think I have it figured out though:

1) Heat shield above the catalytic converter was loose. There are two studs on the bottom of the body and two nuts secure a stamped metal shield. One nut was loose, causing it to bounce around and hit on the nut/body. I tightened the nut down and wedged a piece of 5/8" fuel line between the shield and the body. The hardware is a complete pain to get a wrench to.
Heat shields are the #1 source of weird vibrations in Gen1 Xterras. I'm at the point now where I've ripped out about 90% of them.
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