There has been quite a few issues with "diesel-noise" from the Twin Spark
engines. The "diesel-noise" will in the beginning last only a few seconds
after turning your key to start the engine. But it will last longer and
longer. The "diesel sound" does not have to be quite noticeable as it is the
first few seconds after turning the key. An ok engine should not have any
diesel sound at all, even at cold start!
It's a typical failure of the so called "variator" that regulates the
camshaft timing over the full rpm-range. If damaged it means loss of
"top" power, even less power under 3000rpm and higher fuel consumption.
No matter how old your car is, it is always a "hidden fault". Under
the consumer protection laws valid in Europe it will remain guarantee
for many years.
There should be no problem driving with this, you will not damage
anything, but it should eventually be fixed. In Norway I have heard
that this is fixed on warranty and Fiat even pay a part of the price
if the car is off warranty.
The reason for this is many cold starts and driving short distances.
This is because the variator need oil to get its work done, but after
a cold start it takes some time to get the oil in this variator. This is
a poorly constructed part and has been replaced by a new part with
the part number: 60666199
All new Alfa's since April 2000 have this new variator. The "old" one came
from 2 sub suppliers of which 1 made a bad product. Anyway, your dealer
should know; is was one of there nightmares in 1999/2000.
You can also give your variator a better life if you change oil at least
every 10.000 km (which is recommended anyway).
I have recorded the sound of a bad variator for you to download here.
And here is the sound of my engine with the variator replaced -> download.
Or you can hear sound examples of good and bad variators on
this great page.