Hmm, I thought you'd get more answers sooner, & I started this saga before you'd got any!

But for what it's worth, I'm also pretty sure there is
no vacuum involved in shifting the gears in the SE5's, AFAIK it's all electric solenoids & oil pressure! Can you tell us exactly what it is about your problem/these noises that makes you think the noise is specifically transmission related & not saaaay, something to do with the engine top end?? Is it just the noises relationship with or the timing of your gear changes & the noise occurring? Or something else? :dontknow:
Not positive that I can help you much because I haven't had a great deal of exposure to Spyders with these particular problems, but I can try throwing some random thoughts out there - they might help you, or possibly might prompt a helpful comment from someone else.... one can only try! :sour:
Chattering & rattling noises like those you've described are sometimes associated with a worn centrifugal clutch, but when they are, those noises usually occur or are noticeably worse when changing
UP, not down; & another thing - a worn or dodgy centrifugal clutch will usually tend to make the vehicle
want to move even at idle.... A centrifugal clutch that's working properly normally has to work harder to
DIS-engage at idle than they do to work and 'lock' in order to transmit drive - 'locked at revs' is their 'natural resting state' & everything has to be in good nick & adjusted correctly for them to disengage properly at idle. So when they are in good condition they will generally 'lock up' fairly readily as the revs increase; but when they are in poor or worn condition it becomes harder for their weakened springs &/or worn components to disengage at idle; so that means when worn they tend to want to transmit
some drive most of the time, even at lower revs & idle, & hence they get a tendency to 'creep' at idle as they get weaker & more worn - altho when they die completely, they often won't transmit any drive at all!!
There again, if it's not the gearbox or the centrifugal clutch, maybe your front drive pulley is working loose or running on a damaged spline - it's not an un-heard of problem &
that will generally make more noise when the load is off while you are coasting to slow or changing down thru the gears & also won't usually make as much noise when you are accelerating; at least not in the early-ish stages when putting everything under load means the worn or loose bits all get pulled together under pressure & there's still parts of the spline in the pulley that can still grip the shaft!! :shocked:
Not much definite to go on I know, but maybe just enough to help?! I hope you get it sorted. :thumbup: