UK2

I have recently started to hear a sort of fluttering sound coming from the rear right hand side of the car. It mainly happens when I'm in 1st thro 3rd gears. I have read about this in the past on one forum but an in depth search has come up blank. Can anyone help?...........Oh it's a 2001 Boxter S with 33,000 miles.

Thanks

insite

when your turning, going straight, accelrating, stopping? how fast? how loud? describe the noise better. what is something that sounds similar?

UK2

Sorry for being brief in my initial description. Its when I'm accelerating, going straight or around a corner. Sounds like a piece of paper flapping in the wind.

Turboflyer

OK, stupid suggestion but have you looked under the car yet. I know but sometime folks look for the worst when it is something as simple as a piece of cardboard stuck somewhere. If not maybe some trim piece or plastic aero part under the car. Of course there is always the universals and trans. That is usually accompanied by some type of vibration though.

UK2

Yes, I have looked all over the car, and nothing is flapping. I think it also happens when I just rev the car as well, but I'm currently at work and cannot verify that untill later. It sounds a more metallic than maybe my paper comparison suggests. I seem to remember something about a dodgy MAF causing this noise in the post I have been trying to find but maybe I have just imagined that!!! What does a catalytic converter sound like if any internals are broke???

insite

does it still happen when the top and windows are up? if you put the car in neutral and coast, does it still happen? does the flutter speed up or slow down with the engine or with the speed of the car?

senna21

You'd be down on power initially until the CAT cells begin to deteriorate to a point to allow proper exhaust flow. During that time you'd also hear a rattling emanating from the exhaust tubes/CATs as the blocks begin to rattle around inside. You'd also get some white powder out the exhaust tips.

UK2

Thanks for the replies so far guys. I have just driven it back from work, it's definitely a mettalic sound and it is really obvious in the 1500 - 3000 rpm range, it goes with engine revs not the movement of the car. I think it is exhaust related.

stumpjumper

I had the exact noise you are describing, and at first I thought it was the cat internals

my problem ended up being a broken weld on the permanent heat shields that are on the secondary cat, this broken weld was completely silent when the car was cold and it took me months before I grabbed a rubber mallet and whacked the muffler after a long drive

sure enough there was a slight rattle, at first I thought it was the bolt on shield so I removed it, but the next day the sound still existed

while replacing my wheel bearing (luckily for me on the same side) I removed the cat and found the broken weld on the inside of the bend that the shield makes

these shields provide no structural benefit, they're just 2 steel plates welded together on the inside and outside of the bend, then they're welded in (iirc) 3 spots to the cat can, what I ended up doing was cutting these welds with a rotozip metal cutting wheel (any grinder could do it, but it is tough steel)

suddenly, on my first drive, the car sounded different than I ever remember it, i loved the new to me sound (now the other side has started to do it, I'll cut that off soon)

so my advice, get a rubber mallet, heat up the exhaust on a nice spirited drive, then whack it and listen!

UK2

Thanks Stumpjumper, I'll try that. Might even run it round to the local muffler shop tomorrow

insite

check the heat shielding under the rear bumper, too. it shields the bodywork from the muffler / cats.

perrys4

Silly, thats your motor your hearing!! :-)