Possible wiper issue

[harley141213]

so I just purchased a 61 plate A5 coupe. Today went out in it with the rainfall constantly changing. Had the wipers on 1 st setting and the altered speed in relation to the amount of rain coming down. Great! However suddenly without warning or increased rainfall they suddenly went ridiculously fast, so much so that they hit the windscreen pillar making a loud thud, this made me jump wondering what on earth it was?
Surely that isn’t normal? Anyone else experienced this? The car has 135k up it.

Not sure if something is on its way out? Linkage maybe? Or in need of adjustment?

Thanks
Sean