Noise consistently activates the stress axis, which governs extremely potent biochemical pathways and thus over time can bring about physical changes easily. Especially to sensitive tissues like nerve tissue. This is well established. It's similar with disturbed sleep. For Parkinson's disease specifically, the Guardian article mentions this:

Existing research has found potential biological pathways that link noise exposure to Parkinson’s disease, largely due to stress responses and disrupted sleep.

"Potential", sure, but altogether (i.e. now also including the prospective (!) decade-long (!) cohort study with over three million (!) participants), the causal link is very probable.

Regarding the magnitude observed here, I admit a hazard ratio of 1.04 (so +4%) is not large. Note, though, that it's "per interquartile increment of 8.9 dB". So going up three quartiles (+27 dB, about 7 times as loud) already gives you somewhat above 12% additional risk.

This is territory where it's getting relevant for personal and societal decision-making—especially when considering that Parkinson's is just one disease of many.

oh yes, this is why all rock stars have Parkinson's.

What causes the sound though? Vibrations. Living next to a busy road means exposure to constant tremors, even if low level, which would certainly explains the balance aspect in my opinion.

If this is the actually connection and they know it, then yeah i suppose the headline is being clickbaity and facetious.

However, parkinsons is a brain disease, not just a disease of the nerves - with correlations demonstrated for other environmental traumas (article lists pollution for instance), it seems likely that parkinsons is just the result of a brain traumatised from the combined actions of modern life traumas, which maybe deny it a chance to grow or heal the way it is supposed to.

I guess all i can say is that the reasoning makes sense to me. Human biology is weird, biology in general is weird, and all our civil engineering systems need to be revised anyway for multitudes of reasons, so i am not object to the idea on any basis.