Video and Audio problems on 3 channels, same QAM Freq.

[new2digital]

As of 2 or 3 days ago, we are getting video and audio breakup, macro-blocking and freezes on 3 channels that are on QAM Freq 765 MHz. Checking our primary set, diagnostics show no errors and the levels are fine. Level is 4 dBmV and S/N 37 dB. In the past, these problems have usually occurred when the level dropped to around -5 and the S/N around 30-32. But then, the diagnostics showed Errors (Corr Bytes, Uncor Blks > 0). Not so now. It seems to happen in the morning between 7AM and 9AM and in the evening.
The mess shows up on both our sets ... primary is a plasma on an 8300HD, the other an LED on a 4642.
The 3 channels are 522, 523 and 524 which are ABC, NBC and CBS from Buffalo ... channels that we watch a lot, particularly when there is no Cdn channel carrying the same program.
We are in Woodstock, Ontario. Anyone else seeing a similar problem?