Timing belt breaks: worse case you have a bunch of bent valves, a few pistons with major damage, maybe even more collateral damage to the valve train in the heads.

Butterfly valves: worse case you have scored cylinder walls, broken rings, piston damage.

Either way you are talking a lot of $$$ and time to fix the worse case.

I would take the engine down to the timing belt assembly and inspect the belt, check for proper tension, inspect the water pump seals.

Do a search on the butterfly valves, I seem to remember some one mentioning that they tick or chatter before they let go. I chose to just replace the lower plenum when I bought my used 95 SR so I haven't heard it myself.