[V8] Noise under load @ 1800 RPM

[Ingo Rautenberg]

Based on what you've said, it's gotta be motor mount(s).  Really.  I  
have yet to see the trans mounts fail.  The motor mount's give in  
relation to torque and I'm 95% sure that's your problem.  Otherwise  
you'd have something loose or broken with the exhaust in my  
experience -- but you say the exhaust checks out.  It deifinitely  
fits the "sounds like it's coming from the floorboard" description to  
me.

Now I have had the bolt break that holds the rear diff at the back of  
the car, so that's one other place to look for a load-induced knock.

-Ingo

On Mar 5, 2009, at 9:17 PM, Seamus O'Carey wrote:

> I've been trying to get to the bottom of this noise issue since I  
> bought the
> car.  I thought maybe it was just a loose exhaust hanger, but I  
> just had it
> checked out and the entire exhaust system is solid and all the hangers
> intact.
>
> We did discover, though, that the noise comes on only under load  
> (whether
> accelerating or while standing still with the car in gear) and very  
> suddenly
> just before 1800 RPM, and goes away a little after 2k.  Inside the  
> car, it's
> a loud grumble that you can feel through the seat/floorboard.  What
> confounded us, however, is you can NOT hear the noise from outside  
> the car.
> Not even a hint of it, even with the window open.
>
> The guy at the exhaust shop thought maybe it was coming from the  
> center
> differential, just behind the transmission (even though he listened  
> to it
> with a stethoscope and still couldn't hear anything).  He mentioned
> something about how Subaru owners can pull a fuse that will disable  
> the
> center differential in their cars, which would help them diagnose  
> something
> like this.  Do we have something similar in the V8?
>
> Seamus
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