I am in need of diagnosing a knock my car has had. I've included a video and a detailed text description that I hope will help. I have not run across a problem exactly like this before.


Here is the video of my car making the noise (1 meg)

http://www.sexyracing.com/TWS/knocking.asf


The following is all the info on the problem I could think of.

knock frequency seems to be dependant on speed. Each knock is countable under 8mph, the knock increases in frequency as speed increase.
knock tone does not change (always a low, knocking on wood sound)
knock volume is load dependant with extra (maybe 4x louder) volume in reverse


no noise is made when...
hard accel
hard brake


noise is minimal to none when...
clutch is in
being in neutral
moderate to swift accel


noise is noticeable when...
slow to moderate speed accel in 1st through 6th staying under 3000 rpm (as I climb in the gears the noise softens)

1-2 gear the noise is most noticeable and knocks at a moderate pace
3-4 gear the noise is moderate and fast
5-6 gear the noise is quiet and fast in frequency


noise is loud when...
The sound is very picky about load. While moving forward the loudest I could make the sound was in 3rd gear at low speeds with just a hint of gas. Too much throttle and the sound goes away.



noise is loudest...
in reverse


while in reverse...
knock frequency increases as speed increases, sound fades quickly at 8 mph and goes away at 10 mph when accelerating at a swift reverse speed.



I would rule out...
Engine, Flywheel, 1-6 gears or driveshaft

It is unlikely to be, but still a possibility...
Clutch or Hub

I am thinking it is...
Diff or Axle

 

This is the frequency of the knock in realation to the spin of the wheel. Unless I am mistaken, this almost certainly proves that the problem is somewhere between the back of the trans and the ring/pinion.

 

After even further investigation I found out that the bolts connecting the drive shaft with the diff had backed out slightly. So basically I am down to determining if I screwed up the bearings in the diff or transmission. And it sounds like the diff. I guess there is still the possibility the pinion is damaged. But most likely I need to replace the pinion bearings.

So problem solved.. or at least problem identified.