My 1998 V70 runs as you would expect except that there is a deep loud
resonance on acceleration. When cruising at any speed / engine revs the
car is smooth and quiet but . I've had two exhaust companies and one
volvo dealer look at it and they all say there's no leaks or obvious
fault in the exhaust system. With 270,000 Kms on the clock I would
think the Cat might be faulty in some way and if so perhaps the
resonance would be the result. A suggested fix has been to replace the
entire system starting with the Cat but with the price of Volvo spares
it would be almost cheaper to buy another second hand one without the
problem!
I've checked the timing, changed the air filter for a genuine Volvo and
am satisfied there is no visible fault with the intake system.
Anyone else had similar problems?

I don't know what the problem is John, but I have it too. I bought the
same model about 8 months ago with 173,000 miles and I noticed the same
thing, though mine is a bit louder even when cruising. Because the
sound is throaty and a bit resonant, I don't find it too annoying, but
I would prefer not having it. I asked about it on this forum a few
months back, and at that time the only suggestion was a leaking
flexible connector at the exhaust manifold, but I can detect no leaks.
I will be interested if anyone steps up to the bat this time.

Bill

JohnM wrote:
> My 1998 V70 runs as you would expect except that there is a deep loud
> resonance on acceleration. When cruising at any speed / engine revs the
> car is smooth and quiet but . I've had two exhaust companies and one
> volvo dealer look at it and they all say there's no leaks or obvious
> fault in the exhaust system. With 270,000 Kms on the clock I would
> think the Cat might be faulty in some way and if so perhaps the
> resonance would be the result. A suggested fix has been to replace the
> entire system starting with the Cat but with the price of Volvo spares
> it would be almost cheaper to buy another second hand one without the
> problem!
> I've checked the timing, changed the air filter for a genuine Volvo and
> am satisfied there is no visible fault with the intake system.
> Anyone else had similar problems?

Thanks for keeping me company on this one. I guess you've tried to bung
up the exhaust pipe to see if there are leaks? -that was what the
garages did with mine. One garage listened with a purpose built probe
and went straight to the flexible joint but found nothing.
I once had a problem with an 850 which didn't demonstrate any leak
until acceleration under load when the engine movement was excessive
due to a worn stabiliser mounting. The movement exposed a fracture in
the exhaust manifold pipe, but the noise as quite different to what I'm
currently experiencing.

John