I had an S1 for 2.5 years with manual windows and they never rattled... believe me there will be plenty of other squeeks, rattles and groans but I didn't hear them coming from the windows.
It would be improbable that the latest mechanism (undoubtedly aped from that) would be much different. I think this is just tosh.
There will be more noise coming from the $25 of loose change that will lives under your drivers seat.
That said, some people had their window mechanisms fail on the earlier cars. Personally I think a large part of this was just abuse - or more accurately lack of empathy with a handbuilt Bristish sports car e.g. if the window is stiff and you just wind the bugger without wondering why then it's gonna break. Smart people used to open the door a tad for the final 1/2" when closing after fitting the roof for example.
If you can decorate, fix a leaky washer and maintain a woman I reckon you'll do fine with manual windows. Frankly I'd put my money on them over the handbuilt British electric variety!!!
