It might be rain related - if so:
Go out front of your house next time we get solid rain and it goes out in a permanent feeling way.
Find your Telstra pit... look through the hole in the lid of the pit for water.
If you see water in there - you'll need to make something to cover the pit.
This is what we did, and it fixed our drop outs (it was taking days for the pit to drain so we were without internet for days at a time).