I'm in Bolton - and have an engineering company - 'nothing we can't make' is my internal slogan (get's me into all kinds of trouble, not usually serious

).
I had to leave early yesterday so couldn't reply.
I've had the Emira in to H R Owen in Stockport a few times to try and sort this issue. The technician there can't always hear what I'm trying to describe, but to me it's horrendous. It's also much worse from the driver's seat rather than the passengers as the Sub is directly behind you.
I've stopped listening to the stereo with the windows down (or even just a crack) because, as you will know, it's just horrible if you have this problem.
So, they removed it completely and I went for a drive, and the problem went away - completely.
We discussed simply leaving it out, but it's clearly there to protect from water ingress, (it's really there to stop your windscreen blowing out when you shut the doors - which is handy!).
When they removed mine, it was damaged on one of the clips - so they replaced it with a new one - but it made no difference at all. That's why I think it's actually something else vibrating that the vent flaps exacerbate, and removing the vent stops it - rather than it being the vent itself making the noise. The main reason I think this is that it's the only explanation I can come up with for why all the cars don't have the problem.
Anyway, I have to wait 3 months before it can be released to me (Lotus policy on exchange parts so the dealers don't simply give stuff away).
I'm about 6 weeks to go on that - then we will measure it all up a recreate it - but instead of flaps I intend to have S shaped tubes allowing air movement but no water ingress because the tubes will be predominantly vertical.
It might not work - but I'm a stickler for audio and one way or another I'll find a fix.
These things don't happen overnight - so be patient - but I'll be back when I've made progress
Cheers
Tony