Odd Popping Noise From Rear Axle (2000 323i E46 4-door)

Hello
Im new to this usenet thing so i don't really know the netiquette behind it, i do appologize in advance.
So here is the scenario: 2000 BMW E46 323i 4-door with 81000 miles on it.
This noise has been happening off and on for the past year or so and shops can't figure out what it is. It basically sounds like a "a tennis ball being hit with a racket but more metallic". The popping gets faster as I accelerate but it stops around 40mph. The noise does not happen when i coast, only when i step on the accelerator.
One interesting observation, but hardly scientifically tested is, that the noise went away for a few days and when i went to fill up my tank, I checked my air(last time i checked was around 2 weeks prior) and it was at 28psi. I filled it to 34psi all the way around, and the popping noise came back.
Any ideas?
Also, today I will drive it in different gears (its an auto with "steptronic") and see if it occurs only on particular gears.
Lastly, an off topic question. Has anyone taken out their A/C faceplace? Do you know how far back it goes or is it just a surface thing.
The reason I ask is, I got the crazy idea to remount the faceplace on to two hinges on the bottom so i could hide an LCD where the A/C is, and have the A/C faceplate "pop down" when I want the LCD screen to appear. Just an idea.
Thank you all very much for your help.
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On 5 May 2007 10:24:39 -0700, " snipped-for-privacy@gmail.com"

Stupid question but have you got the same size tyres on both back wheels?
Have you checked the diff oil level lately?
Sounds a bit like CV joints on the rear drive shafts. Remember thes do wear on oneplace only and when the car changes attitude on acceleration they move to a slightly different angle and the balls will ride over the wear ridges and sound like metallick clicking.
The rear drive shafts would be the first thing I would investigate followed by the propshaft then the diff unit - you might have a broken tooth on one of the planetry idler gears or even a worn thrust washer/bearing.
Steve
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Yep same tires on all four wheels. I don't want to distract but one of the "nuts" is missing on the left wheel.
I shall check the Diff (I assume is Differential) Oil and then take this checklist into the shop and see what they have to say.
and CV stands for?
Lastly I will see if faster or slower accelerations with more attitude change will activate or deactivate this.
Oh....also, I drove in different gears and the popping was intermittent in all of the gears. Maybe less when i accelerate from 4 or 5, but that could be because the car's attitude changed less.
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Constant Velocity Joint. It's the two universal joints that are on each end of the half-shaft (one near the differential, one near the wheel). They click when they wear out.

You know, it's possible that you have a rear subframe mounting bracket problem. Some E46 cars have had the metal where the bolts holding the subframe (it supports the differential) break. The popping noise could be that. Go to: http://www.turnermotorsport.com/html/detail.asp?PRODUCT_ID=TDR4675412 and see if any of the pictures look like your under-body.
FloydR
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wrote:

If you have the alloy rear subframe then these are known to corrode and break?
Definitely worth a good look!
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