Multi-Path solved by up-graded outdoor antenna
Antenna is probably marginal and traffic causes multipath/signal loss.
Mount an antenna above the roofline at least 30 ft up.
Jim is right. You are suffering from Multi-path.
Multi-path signals reaching the antenna out of phase can confuse the ATSC (Digital) chip set in the converter box (or digital TV tuner sets).
If the signal reaching the front of the antenna is not 2 to 3 times stronger than a bounced signal from the same station reaching the back of the antenna, the ATSC chip doesn’t know which signal to use, so it just keeps searching. The answer is to up-grade to a new digital outdoor antenna, the higher, the better, tuned to receive digital signals and help reject Multi-path signals.
While it’s correct that antennas can’t tell the difference between analog and digital signals, there are definitely certain models which have higher DTV batting averages than others. Not all antennas are equally suited for DTV. A percentage of viewers will require something a little more tailored for DTV reception.
The correct digital age outdoor antenna installed and aimed properly, will receive the desired local stations it’s aimed at. The more powerful the antenna, the further from the towers your antenna can be located, up to 70 miles or more.
Signals bounce off many things, such as buildings, hills, even walls inside the reception room and yes, cars, in the case of an indoor antenna. But sometimes a bounced signal can be stronger than trying to receive the signal straight on. If you’re going with a indoor antenna, try several different locations and directions in the room.
With a new digital age antenna, you may also be able to receive out-of-town channels, carrying blacked out sports programs, almost completely uncompressed HD broadcasts (unlike cable or satellite) or network broadcasts not available in locally. As an added benefit, an OTA antenna provides reception for second sets in homes or apartments not wired for whole-house signal distribution.
Depending on the level of desire to receive an excellent picture, almost completely uncompressed digital and HD signals and multiple broadcast signals, considering the investment in TV entertainment you've already made, you should consider up-grading to a new Digital outdoor Off-Air Antenna. Buy your new antenna from someone who will refund your purchase price, no questions asked, until you find the right antenna.
You can go to antennapoint.com to see quickly what stations are available to them, the distance, UHF or VHF and compose heading to help in choosing and aiming their antenna.