Hmmm... okay. I get a lot of bogus signals while driving and constantly have to nudge it to continue scanning. Part of the issue is I don't have an antennae on my vehicle, but I'm sure this would continue even with a stronger antennae as it would just find weaker signals. Thanks for the explanation.
Unless you are receiving noise from inside your vehicle. It would not be out of the ordinary for noisy electronics in a vehicle to be picked up by your scanner. An easy way to test this would be to find a place where your squelch opened, and park there. Try shutting the engine off, all the way, pull the key out, open the door and close it again to shut off all accessories and see if the noise remains. You could also try getting out of the vehicle and see if the noise gets stronger. If the noise/interference is coming from your vehicle, then an outside antenna would likely help. If not, one could still help as it would reduce the sudden changes in signal level.
Or, like you suggesting, just setting the RF squelch to hide this stuff would work, too.