I agree with Ed and think it's best to use a heavier regulator, or maybe throw some of the power into a series dropping resistor or Zener diode.
Regarding spurious noise and oscillations, here's something I wrote in time-nuts a few months back:
"It's a bit tricky to use prescalers for arbitrary input signals. As others have mentioned, they self-oscillate when there isn't a valid input signal. This is not only a possible, but nearly certain characteristic due to the (typically) ECL input amplifier being biased right at the logic threshold, followed by lots of gain, then divided by flip-flops. These were typically used in PLL synthesizers over limited frequency ranges, with known, adequate power levels.
If you are counting strong signals at well defined DC levels, you can use ECL directly with proper biasing. For a general purpose counter, you want lots of sensitivity and wide frequency range, so the usual prescaler with self-biasing and AC coupling is a simple way to go. You just have to be aware of the limitations. You can eliminate the oscillation tendency by giving up some sensitivity, but it's easiest to just ignore it unless it causes trouble."
Ed
