Interesting one this. I too have weak signals on a couple of frequencies. All channels on these two frequencies are terrible. The thing is though, I have two of these boxes and the latest one I bought from tmc is perfect with strong clear channels on all frequencies.
The other thing is that on the older box with the bad frequencies, I have to load the firmware from October as on the last couple of versions, I have real trouble, missing most channels after many scans. My thoughts are that I have a weak or faulty tuner on the older box but does anyone else have these problems?