Ideas on a noise, please

[insite]

i always hate trying to diagnose a funny noise from text, so i'll do my best to describe this. i'm just trying to get a list of ideas to help me find the source of this noise. as an FYI, two weeks ago i did the clutch, flywheel, axle rebuild, and exhaust. one week ago i was at the race track.

the noise sounds a little bit like a helicopter in the distance; it's not very loud, but it is a little audible over my exhaust.

it seems to come from the right rear of the car.

it increases frequency with vehicle speed, NOT RPM.

it ONLY occurs when the engine is under load (even a teeny, tiny bit of load).

it does NOT occur when coasting in neutral, driving in gear under no load, or decelerating in gear under engine braking.

it occurs in any gear.

any ideas are appreciated; this is just a brainstorming exercise. thanks.

[rsfeller]

Sounds like a bearing or CV joint...although since it goes away I doubt it's a bearing. Bearings tend to rumble all the time. CV joints can make their funny sounds (usually clicks while turning) while only under load. They often go away while coasting.

Shawn

www.carboncow.com

[insite]

Sounds like a bearing or CV joint...although since it goes away I doubt it's a bearing. Bearings tend to rumble all the time. CV joints can make their funny sounds (usually clicks while turning) while only under load. They often go away while coasting.

Shawn

www.carboncow.com

so far that's my guess, too. unfortunate since i just serviced the joints. oh well.

still taking ideas just in case....anyone?

[rsfeller]

Your recent service may very well be good but I would NEVER count out the failure of a recently repaired part due to human error. I've seen CV joints damaged prematurely from poor lubrication or installation.

I buddy of mine lost a $100K Formula boat this last summer due to human error of the dealer due to poor install of a regular maintenance item, the outdrive bellows. This is a boats version of a CV boot and human error was the fault.

Never count it out until you have personally inspected.

[insite]

Your recent service may very well be good but I would NEVER count out the failure of a recently repaired part due to human error. I've seen CV joints damaged prematurely from poor lubrication or installation.

I buddy of mine lost a $100K Formula boat this last summer due to human error of the dealer due to poor install of a regular maintenance item, the outdrive bellows. This is a boats version of a CV boot and human error was the fault.

Never count it out until you have personally inspected.

ah, didn't mean to infer that i'd discounted personal error here. the 'oh well' comment might as well have been 'c'est la vie'. whenever something breaks, the FIRST place i look is to what was most recently done on the car. in this case, i'd had the axles off and the car was making a speed sensitive knock. in my mind, this is where probability says the problem is. still, though, i like to generate possibility lists before i dive in so i can check everything in one shot.

[ocblubox]

i always hate trying to diagnose a funny noise from text, so i'll do my best to describe this. i'm just trying to get a list of ideas to help me find the source of this noise. as an FYI, two weeks ago i did the clutch, flywheel, axle rebuild, and exhaust. one week ago i was at the race track.

the noise sounds a little bit like a helicopter in the distance; it's not very loud, but it is a little audible over my exhaust.

it seems to come from the right rear of the car.

it increases frequency with vehicle speed, NOT RPM.

it ONLY occurs when the engine is under load (even a teeny, tiny bit of load).

it does NOT occur when coasting in neutral, driving in gear under no load, or decelerating in gear under engine braking.

it occurs in any gear.

any ideas are appreciated; this is just a brainstorming exercise. thanks.

Did you remove the exhauxt mainifold? I remember my 3 series BMW had a simialr sound when there was a leaking gasket on the manifold allowing the sound from the cams to come through

[insite]

Did you remove the exhauxt mainifold? I remember my 3 series BMW had a simialr sound when there was a leaking gasket on the manifold allowing the sound from the cams to come through

i did actually remove both exhaust manifolds & replace them w/ headers. i'll check that, but i'm not sure it's the problem since the noise gets faster with vehicle speed rather than engine speed.

[John V]

i always hate trying to diagnose a funny noise from text, so i'll do my best to describe this. i'm just trying to get a list of ideas to help me find the source of this noise. as an FYI, two weeks ago i did the clutch, flywheel, axle rebuild, and exhaust. one week ago i was at the race track.

the noise sounds a little bit like a helicopter in the distance; it's not very loud, but it is a little audible over my exhaust.

it seems to come from the right rear of the car.

it increases frequency with vehicle speed, NOT RPM.

it ONLY occurs when the engine is under load (even a teeny, tiny bit of load).

it does NOT occur when coasting in neutral, driving in gear under no load, or decelerating in gear under engine braking.

it occurs in any gear.

any ideas are appreciated; this is just a brainstorming exercise. thanks.

This sounds a lot like an axle to me. When the axles are loaded by the engine the bearings are in a different position than when you're coasting or decelerating. It sounds like the axle has some FOD in it or it's just worn out.

John

[insite]

This sounds a lot like an axle to me. When the axles are loaded by the engine the bearings are in a different position than when you're coasting or decelerating. It sounds like the axle has some FOD in it or it's just worn out.

i'm inclined to agree....hopefully my ears are good and it really is the passenger side, otherwise, i'll be buying two.

[insite]

i'm inclined to agree....hopefully my ears are good and it really is the passenger side, otherwise, i'll be buying two.

well, as luck would have it, murphy hath struck again. replaced the inner passenger side CV joint and the noise still occurs. i've since had a chance to ride in the passenger seat with someone driving. from the driver's seat, the sound is on the right. from the passenger's seat, it's on the left. going to replace the other inner CV joint & hope that cures it. if it doesn't, i'm concerned that the only other driveline component that sits between the driver & passenger is the transmission.....

question: when trying to ascertain which CV joint was bad, does anyone have a good method? i THOUGHT i'd be able to use an IR Pyrometer to take the temperature of each joint & replace the one that was really hot. oddly, none of them are really hot. after a long drive, they're all about 140F.

[ninenineseven]

i'm inclined to agree....hopefully my ears are good and it really is the passenger side, otherwise, i'll be buying two.

well, as luck would have it, murphy hath struck again. replaced the inner passenger side CV joint and the noise still occurs. i've since had a chance to ride in the passenger seat with someone driving. from the driver's seat, the sound is on the right. from the passenger's seat, it's on the left. going to replace the other inner CV joint & hope that cures it. if it doesn't, i'm concerned that the only other driveline component that sits between the driver & passenger is the transmission.....

question: when trying to ascertain which CV joint was bad, does anyone have a good method? i THOUGHT i'd be able to use an IR Pyrometer to take the temperature of each joint & replace the one that was really hot. oddly, none of them are really hot. after a long drive, they're all about 140F.

I'm a newbie here but just thought to ask if you have checked your tyre pressure? I know it sounds dumb but there has been some discussion in the 996 forum ref transmission noise;

http://www.renntech.org/forums/index.php?s...nsmission+noise

Just thought to add that in-case you hadn't thought about that one??

Cheers,

NN7

[insite]

i'm inclined to agree....hopefully my ears are good and it really is the passenger side, otherwise, i'll be buying two.

well, as luck would have it, murphy hath struck again. replaced the inner passenger side CV joint and the noise still occurs. i've since had a chance to ride in the passenger seat with someone driving. from the driver's seat, the sound is on the right. from the passenger's seat, it's on the left. going to replace the other inner CV joint & hope that cures it. if it doesn't, i'm concerned that the only other driveline component that sits between the driver & passenger is the transmission.....

question: when trying to ascertain which CV joint was bad, does anyone have a good method? i THOUGHT i'd be able to use an IR Pyrometer to take the temperature of each joint & replace the one that was really hot. oddly, none of them are really hot. after a long drive, they're all about 140F.

I'm a newbie here but just thought to ask if you have checked your tyre pressure? I know it sounds dumb but there has been some discussion in the 996 forum ref transmission noise;

http://www.renntech.org/forums/index.php?s...nsmission+noise

Just thought to add that in-case you hadn't thought about that one??

tire pressure is good; thanks for the idea.