low upstream snr causing lost sync's?

[#1]

Since getting a new router that reports the upstream snr, I am wondering if it can be the cause of lost connections with the exchange?
I have a interleaved line and am happy with the speeds I get, if the connection is stable.  So about a month ago someone/BT's system/tooth fairy removed interleaving and I noticed that when the upstream SNR dropped to 6 or below I would suffer multi lost sync's.  So I had to get interleaving back on just to have a stable connection and wonder if its the fact that the upstream is dropping to a low figure that might be a cause.
Yesterday case in point, my upstream again dropped too 6db even though I am suppose to be still interleaved[ticket open to check if so] and since then my router has lost sync again after being stable for nearly 3 weeks, with the only dropped PPP sessions by my self to gateway hop after finding routing to USA an issue on some of them.

[#2]

Hi Gus,
Interleaving is definitely enabled both up and downstream, that's to say it's actually on rather than being set to Auto. Not sure why the SNR is dropping like that, though it suggests some kind of noise or interference on the line either from maintenance or more likely something electrical near the line.