The left-hand pillion footrest on Paralever GS BMWs is bolted directly to the exhaust silencer, as is the pannier strut. This is a strong and reliable arrangement, but it does nothing for the comfort of the person sitting at the back, who will soon wonder why their left foot has gone numb and what that army of buzzing fire ants is doing crawling up their leg.
So yes, there is a lot of uncomfortable, high-frequency vibration that gets through to the footrest. We had tried curing the problem with a huge, industrial silent-block, but all that did was make the footrest fold downwards, which is unstable, dangerous and ultimately just as uncomfortable.
There is an after-market bracket that's available from a few retailers, we bought one to try, and while the concept and execution are sound, it does require (I think) stock rider footrests, which we don't have, and possibly removing the left-hand side panel, or a different exhaust silencer altogether.
Now take a look at this: