2004 BMW 325 Thud/Thump/Knock sound related to throttle inp

  • 2004 BMW 325
  • 6 CYL
  • 2WD
  • 83,000 MILES

I recently took a long trip (out of state) and this is when the noise started. It must have been 3-5 hours into the trip when it happened. Prior to the trip, the serpentine belt, a/c belt and front lower control arms were replaced.

The noise commonly occurs past 40mph. It is more prone when in the later gears. 5th, 4th, rarely 3th. Once the car is rolling, the noise will occur if the car is decelerating, as soon as the throttle is depressed, and the car accelerates. A faint, but clear thump/thud sound will come from the front end, close the the pedal area around the foot well. The noise will also occur when letting off the throttle under harder acceleration, and on the higher gears as well, but it's not as apparent. It is easier to reproduce when I downshift from 5th gear, let the clutch out, and depress the gas pedal. The noise will occur almost immediately after throttle is applied. The faster the speed, the more apparent the noise becomes. It's not RPM dependent.

It appears the noise is related to loading/unloading torque from the drive train. I have researched and come up with suggestions to replace the guibo (flex disk on the drive shaft), and the center support bearing. I inspected the driveshaft, and the guibo does not seem to have any signs of wear whatsoever. I checked the driveshaft for play, and there is some movement but it comes from the transmission. The tranny was in neutral at the time. No play from the guibo. I was unable to see the center support bearing since it was covered with the heatshield.

The motor mounts and tranny mounts were also replaced about 2 months before this started.

Also, prior to the problem starting, I had heard several noises coming from the same place like a stud/nut/bolt came off and hit several metal/aluminum components until finally falling off the car. (This is a very subjective explanation) A few hours later my clutch started chattering, possibly due to extensive driving and this kept going on for 2-3 days after. The chattering ultimately stopped and has not been troubling since then. (Keep in mind I drove to a much warmer state, compared to where I'm at, 65 degrees average vs. 85 at the time)

I visually inspected the control arms, anti-sway bar links and and did not notice any anomalies. I also considered the tie rods but I'm not sure they would cause this symptom.

Any ideas are greatly appreciated.
Do you
have the same problem?
Thursday, April 30th, 2009 AT 10:09 PM

1 Reply

Inspect the driveshaft and report back.
Was this
Saturday, May 23rd, 2009 AT 10:51 PM

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