Hi all

My car has developed a very annoying sound coming from the ventilation system.

There is a constant ppppffffff ppppffffff sound coming from the ventilation system.
At first I thought it was the blower motor or it's bearing doing the noise.

But the thing is that the noise only comes on after the engine of the car is warmed up and also when the engine is on.
When I shut down the car's engine, and turn the key to enable the ventilation no noise appears other than the usual blower sound.

Other thing is that the noise has always the same pitch and frequency regardless of the blower speed. That should render the Blower and its motor as not being the problem.

Ideas, anyone?

It is the air con settling? Both my Fattys have made the same noise for years. Its almost like a slow periodic air discharge through the facia vents but settles down after a few minutes.

If I recall it happens when the air con is first activated (which will be on engine firing if the air con is on by default)

Whilst I say both mine have done it does not mean its correct mind you.  405 AB exec seats Baltic and Cirrus
93 RR Classic efi

Remember it's easier to get forgiveness than permission!

Gone in order:
4.4 TDV8 SE - gone to a good home
93 Classic hard dash Plymouth Blue
03 L322 Oslo Blue
2000 Disco TD5 ES Epsom Green
98 P38 Rioja Red
89 Classic Cairngorm Brown

I've been testing it more over the weekend and the issue seems to be connected with the aircon system, hence the fact it only does it when the car is warmed up and/or with the engine running.

Seems to happen only when the computers want to mix cold AC air with the Hot engine air to maintain the temperature, as until the engine is warmed up, the system is just pulling hot air. After, that it starts puffing away.

After some testing and head scratching, when I disconnected the AC via the dash button, the noise stopped, leaving only the blower noise and no pffff pffff. So, i'm looking at maybe a leak in the system or other thing much worse..