TELECOM 247

Re. internet. When I dial-up my modem makes the usual faint
screeching/scraping noise but then it stops and makes an
echoing ping sound before continuing with its screeching.
Since this ping noise started my connnection has been very
slow - never more than 38k. BT say theres nothing wrong with
phone line, I assume they must be right, but I cant find
anything wrong with my computer hardware either. Any ideas
as to what is going wrong? Voice calls work okay. What is this
pinging noise on the line?
Ellie