Elderly next door neighbour has just been round, her BT landline is not making it's usual standby dial tone, instead it's more of an up and down "police siren" type tone. Phone works ok for calls in and out and contacted the BT automated fault service who tested the line and they say it's ok. Unplugged all the phones and tried my phone ( which works fine in my house ) and got the same iffy dial tone. She's got early onset dementia and is starting to get a bit worked up, thinking someone is trying to get through and she may be running up a massive bill. Anyone got any ideas ? A call from a BT engineer will cost £130 if the fault's in her property.