Weird AUII XR8 rattle

[undertow]

Had this noise since I bought the car a few months ago. It hasn't gotten any worse or caused any problems, but it's irritating and I figure someone else might have had this before.

My AUII XR8 (auto, 180,000 kms) has a weird light metallic rattling sound while driving that seems to come from the gearbox area or rear of the car. The best way I can think of to describe it is like hundreds of crickets chirping together! It is not loud but noticable with the windows down or up on a smooth road with the stereo off. Does not rattle when the car is stopped, and starts to be noticable at about 30km/h, then stays about the same volume from 40km/h through to 100 (at which point the wind noise starts to drown it out). Does not vary with engine rpm/gear changes, but usually gets a bit louder when accelerating gently and quieter on overun. Can still be heard with the tranny in neutral. The pitch/tone doesn't vary with speed either, it stays about the same.

Sounds a bit like a vibrating heat shield or cat, but it doesn't rattle when I rev the engine in neutral. Does not vary in pitch with speed, which suggests not diff bearings. Does not vary with engine rpm, so it's not torque converter bolts etc.

My thoughts are maybe CV joint, wheel bearing or uni joint, but I would expect these to vary in pitch/tone with speed. Anyone come across something like this before?

Thanks for any help.

[HLC]

carbon canister??? but thats in one of the front wheel archs IIRC.

[disco frank]

Originally Posted by HLC

carbon canister??? but thats in one of the front wheel archs IIRC.

yup it is


get under the car when it is on stands and check the heat shield around the cats as they are pretty close to the gearbox


the engine does move on the engine mounts slightly when in gear and this could cause the exhaust pipes to move just enough to cause the rattle

[SSD-85]

carbon canister is, as HLC said, passenger side front wheel arch. The OP is saying its more the gearbox/rear of the car. Also the OP said it does not variate with engine rpm, carbon canisters rattle more rapidly until no longer audible as engine rpm increases.
The fact it does happen when the car is stationary in neutral, eliminates diff, wheel bearings, etc and in most cases the carbon canister, as its audible in this state.

Be sure to thoroughly check the noises' location. If it is definitely NOT the front passenger wheel arch, id be looking at the exhaust system.

[undertow]

Thanks guys.

I just went over the exhaust with a rubber mallet and couldn't hear any rattles. Doesn't rattle when the car is stationary in neutral. Thinking it might be something loose in the gearbox or diff. The pitch of the noise doesn't change with speed, so I don't think it's a bearing. Sounds a llot like a heat shield rattle, but doesn't do it while stopped and I can't reproduce it by wacking the exhaust anywhere! It's got me stumped, so I think I'll keep driving it, and if it's something worth worrying about it will make itself apparent sooner or later...

What sort of noise do rear-drive CV joints make when they wear out? Clunking noises like front wheel drive ones? Also, anyone know roughly how many Km's we can expect out of the AU IRS CV's?

Cheers.