Threepointtwo

I am new to posting on the forums but have been getting valuable information here for years. I have a 97 Boxster that has a very puzzling noise in the drivetrain. The following are the symptoms:

There is a noise that sounds like a flapping sound (as opposed to a click).
The noise is independent of the engine and only comes when the car is moving.
As I start in first gear, is starts flapping as I gain speed.
The noise goes away when I push in the clutch to shift.
The noise comes back in second gear and all subsequent gears.
The noise is not present when in reverse.
However, the noise comes back when in backing up and I push the clutch in.

Any ideas on where to start?

terbiumactivated

Does the noise increase and decrease in speed as the car increases or decreases speed or is it static in nature? How many miles are on the entire clutch assembly? The noise going away when you depress the clutch makes me wonder if the problem is related to the clutch release or "throw out" bearing.

extanker

have a mechanic put the car on a lift and start with the usual suspects ...half shafts etc

Threepointtwo

OK, thanks for the responses. The noise is directly proportionate to speed. I think the clutch and components may not be related because the noise is not there in reverse but starts when going in reverse and the clutch is pushed in.

I have replaced both half shafts since they were due (100k miles) but the noise is still there.

I have posted a short video on YouTube:

Macster

After viewing the clip, listening to it, my WAG would be half shafts, the CV bearings.

You say you replaced these though.

I could then guess wheel bearings but it would just be a guess.

You need or I should say I'd advise you to use a mechanic's stethoscope and as best you can pinpoint where the noise is coming from. Be sure the car is safely and securely supported. A real auto lift is ideal for this. So this means you need to get to the car to a shop.

Anyhow, listen to the car at various places from underneath the car. Is the noise from inside the bell housing? The transmission or differential housing or further out towards where the half shafts connect? At the wheel hub? Listen wherever you can and can listen safely.

Knowing from where the noise is coming from helps you and a mechanic to know what the noise is what it means.

insite

do you hear it coasting in neutral, or only when you're in gear?

Threepointtwo

I am not sure if bout coasting in neutral. I have only coasted with the clutch in and in gear. I will try it tonight.

Threepointtwo

OK, I test ed the car and there is no noise while coasting with the car in neutral. Also, the knocking is only present when under power. When I let off the gas, the noise goes away until I give it gas again.

terbiumactivated

It's speed proportionate and is only present when the drive train is under load and you did both CV joints already. If it were me I'd start by rechecking all the work you did, as you disassemble things look for any wear marks, every time it clunks it's leaving DNA of the problem somewhere. The wheel bearings are not a bad idea but they should make noise when the car coasts.

Threepointtwo

Yes, this makes sense. Rather frustrating issue. It only makes noise under a load in the forward direction and only unloaded in reverse.

insite

i think it's your pinion shaft or your ring gear in your transmission. i have been through this w/ my box. it was impossible to tell whether it was coming from the left or the right.....because it was in the middle. just like you, i replaced all the CV joints....twice. finally a guy who knows transmissions took a listen & made the call in five seconds.

easisest thing to do is swap out the tranny for one from a wrecked car. since your car is a 5-speed, you can get one for around $500 off ebay (last time i checked).

landrovered

Time for a limited slip diff!

insite

that would be good if the issue is just the ring gear. more often than not, the pinion is also damaged, which means major tear down.

Threepointtwo

Great suggestions, thanks for the help. Yes, it is something coming from the box somewhere. A trans swap doesn't look too daunting.

insite

trans swap is very easy in this car; the accessibility is great. the first time you do it, do yourself a favor & pull the rear bumper first. i can get the trans out of my car in under 40min now.