Noise is seen in PAL mode but not in NTSC, could the loop filter be responsible? Should loop filter change depending on whether NTSC or PAL is used?
I've never heard of a different loop filter configuration based on your output format. There is certainly no recommendation for that. That filter is for the internal PLL. I suppose it's possible that problems with the loop filter could create noise on one format and not the other, so could the output filters between the DACs and the output connectors or the analog power supply.
I don't know of any reason to suspect loop filter more or less than the others though.
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