The bumper is actually to keep your strut from bottoming out. Are you running stock springs? It could cause a knock if you hit a rather large bump. I wouldn't think it would on smaller bumps though.

On my old Impreza I had an odd knock in the suspension and it ended up being the strut top was bolted down at an angle. Loosened it up reposition the top and bolted it down, good as new.

Buster
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