Petrol sounds like a Diesel

[Rusty2009]

I have 2  astras both with 1.6 petrol engines, one is auto and one manual
both of these engines are smooth and quiet, I can drive up behind people without them hearing me coming!
without hearing your noise, its hard to say what it is.
it could be a blowing exhaust manifold or a noisy alternator or something else
best get someone to have a listen, do you have a friendly garage?
or did you buy it from a garage? if so maybe they would like to comment?

I also used to have a Civic (spooky)

This reminds me off when I had Astra-G 1.4 drove up behind someone that was stood in the middle of the road and I blasted the horn damn I've never seen anyone jump so far in my life .

Sorry off topic