DirecTV's downlink frequency is in the 12.2-12.7GHz range, so there shouldn't be any interaction between that and your 2.4GHz wireless network.
I would inspect all of the TV connections, particularly the grounding block, for corrosion, tightness, etc. I'd also recheck the antenna's alignment; a bird bumping his head on your dish could move it enough to make your signal pretty weak.