If that indoor antenna is amplfied there is a chance you're overdriving the tuner, basically getting too much signal. But I also know that with rabbit ear type antennas, they generally perform poorly for digital reception, and it's hard to get all the channels with it pointed in one direction.
One easy way to test if your getting too much signal is to put a splitter behind the TV to attenuate, or reduce the power of the signal. If you get a better signal, than you were overdriving your tuner. If it's worse than it's the antenna.
The other possible problem would be that your so close that the transmitters are coming from different directions. Check
AntennaWeb with your street address and zipcode, to see if they are coming from the same direction.
Your best bet is to put an outside antenna up. At your mileage this would call for a small antenna such as a the
DB2 from Antennas Direct, you can keep it low profile by mounting it on this
J-Mount. This antenna picks up about 90 degrees wide, most antennas only pick up 30-40 degrees wide.
-Mike