Media Bias and Polls

It is my completely unresearched impression that the GOP generally polls better during election season than other times. I wonder whether this is because media bias has a much greater effect away from elections, when the politicians have much less reason to invest effort to counteract the establishment media and voters have much less willingness to seek out alternative news sources. This would suggest that when using current polls to predict election results, one should give the GOP a little bump. It also suggests that media bias really doesn't help the Democrats much.