The air extractor noise is a bit different to other sounds in flight, perhaps a quieter version of a gear door being open.

How strange. The vent should have nothing in common with an engine compartment.

Unfortunately, a casual attitude towards fuel in composite aircraft can end in tears. For example, ASH25M VH-GSI returned to Germany for a year and a half to get rebuilt.
After my friend's incident, I asked Rex Mayes to install a Safecraft extinguisher in my then ASH26E. It's likely the first fire extinguisher installed in SLSP and documented on the ASH26E Tech Pages, linked from the ASH26E/31Mi newsgroup.
There is a firewall, whether a good one or not. Definitely not if you drill holes in it.
Jim

On Tuesday, November 24, 2015 at 12:20:13 AM UTC-8, Tango Whisky wrote:

Is that not a firewall?

Why would an engine stowed away in the engine compartment catch fire?! And if it could, why is there no fire sensor installed? So no, it's not a fire wall.