Keith,
Sounds like the "knot" in the back has slipped and is not pulling the rudder down before the bungee/strap assembly in the inside is hitting something, probably the front pulley. Open the back hatch and you should have 4 tubes (2 on each side). Should be held in place with a plastic padeye on each side. Inspect and probably retie tighter the down line (with the rudder deployed). remember, the lines will tighten another 1/4 - 3/4" when put back on the sides with the padeyes
After installing a few up/down pulls when they were new (retrofitted) I got spoiled on them engaging just so.
Also, easy to "feel" any changes when the all are "tweeked" the same. It's also nice for the up pull to engage within a couple of inches of starting to pull.
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Hobie Island Sailing since 2006