Sounds like I'm going to have to find a way to get my head under the dash by the flappy vent and have a good look. (Not so easy with a frozen shoulder, back trouble, knee trouble etc! I seem to be suffering from more than my fair share of 'tempus fugit'
<sigh>) It would seem to be a bit of a coincidence that it's doing it on both sides, though.
I forgot to mention that it doesn't have a sunroof, otherwise that would certainly have been a prime candidate! Good call, though.
I've actually just wrapped my hosepipe up for the winter now that the frost has arrived but, yes, that is probably the best way to find it... if I can borrow a friend to help me that, sometime.
I don't think I'll be doing anything in the next day or two, however, given the weather forecast!