Electrical equipment such as motors, automobile ignition systems, computers, appliances, etc. generate radio frequency noise in various amounts. The noise tends to be concentrated at frequencies in the range of VHF and lower frequencies. The result is, there is more man made noise/interference affecting the Low-VHF channels. The exact amount depends on how many sources there are and how close they are to the receiving antenna. In a rural setting, with underground power lines, the noise level will be lower than in a dense urban or suburban location with many cars, computers, motors and overhead power lines. Generally, the estimated noise in the L-VHF band runs between 10 and 20 dB. The lowest channels tend to be affected the most.
For a general discussion of Low-VHF reception, please see:
http://forum.tvfool.com/showthread.php?t=2858