"Simon" > wrote in message
...
> My car (2001 Chev Impala) makes a kind of hissing noise while accelerating
> (together with loss of acceleration power and worse gas mileage). It's
> getting louder and louder. Many advices from the groups suggest it must be
> from Catalytic Converter. But my dealer says it's not the converter based
> on their test, and it's normal!!!!!!
> The cat converter seems located in the middle part of the bottom. To be
> sure it's the converter, can I do this way:
> - get one person press gas pedal when the other foot on brake,
> - get my ears to the ground close to the converter to listen........
>
> If it's workable, could cause any damage to the car?

It surely sounds like an exhaust restriction--if not the cat conv., then
perhaps a collapsed interior wall of the exhaust- or tail-pipe. Haven't
experienced but one in recent years, altho' it was somewhat common on some
70's models.
Also check to ensure there is no crushing of one of the pipes from having
hit or *bottomed out* on something. HTH, s