Guttural Noise From Under Carriage - 2000 Concorde LXi

Over the past two or three months I've noticed a brief, deep, rumbling
sound - like a loose heat shield (so I'm told) - coming from under the
car just just as it accelerated from stop, under load (hill or
incline). Doesn't last long and is most noticeable when the engine is
cold.

I used to think it was coming from the back so I put a piece of foam
just behind my rear license plate when I washed the car last and heard
what I thought was a similar rattle when the sponge caught a corner.
My imagination must have made it go away...for a day or two. Then I
began hearing it again.

It does seem to have grown louder, though, I doubt if the noise can be
heard by someon outside as I pass them. Today I tried focusing on
which end of the car it was coming from. With the sound lasting no
more than three or four seconds, I located it in the front, underneath
me, and in the back again. In short... I don't know where the hell
it's coming from other than under the car.

A friend who has some experience in these matters ruled out a leaking
head gasket and exhaust manifold gasket; two nightmare that could
throw my little "renovation project" with this beast into the category
of "no longer cost justifiable."

My hopes were renewed when those cradle bolts were replaced without
incident and I began looking forward to holding onto this car and
replacing struts and tires knowing full well I'd be faced with an air
compressor maybe next year or the year after. If this noise turns out
to be something significantly expensive, I'm going to have to rethink
everything. Hope that's not the case. I've grown fond of the car over
the years though I wasn't so five or six years ago.

Would appreciate receiving a list of things this noise could most
practically be so I can decide if that vocational school could tackle
it. I doubt if I can even get it in for them to look at ''til after
the holidays.

 

it happens very seldom, but a couple times i have heard a growling that
sounds like its coming from the transmission. it hasn't set the MIL light
and set no codes, so until it happens again i just take care of it like
always.

next time you hear it see if it seems to coming from under the floor, close
to the center of the car.

 

????

And if it is found to come from under the car close to the center of
the car? A deep rattle (like a heat shield) from a transmission could
me??? (bucks)

 

MIL light<<
????

And if it is found to come from under the car close to the center of
the car? A deep rattle (like a heat shield) from a transmission could
me??? (bucks)"


if you hear it there, we'll want to determine if it is, or if its from the
differential inside the trans, or some other item nearby.


MIL = maintenance indicator light

????

And if it is found to come from under the car close to the center of
the car? A deep rattle (like a heat shield) from a transmission could
me??? (bucks)

 

I thought it was Malfunction Indicator Light.

 

ok maybe so......

 

Could it be a heat shield around any of the exhaust system? Sometimes the
tack welds come loose.

 

Anyone or any small animals missing in the neighborhood?

 

Rather than an external heat shield as has been suggested, it may be
baffles inside a catalytic converter that have come loose and are
rattling. Common noise on the LH cars.

 

ah yes. mine makes a ticking sound these days as it warms up. so yeah
that could be as well.

 

OK. Heat shields and baffles inside the catalytic converter sound like
two possibilities. I'll use them as starters for the discussion I plan
to have with the mechanic tomorrow. Thanks guys.