my customers has a line that sometimes gives a high pitched dialtone and if you call out when it has the high pitch dial tone the voice sounds machine like. hard to understand. this can also happen on incoming calls. when it does there is no caller id on the line. any ideas what causes this. thanks. dave

Have a look at the Sandman diagnostics chart. It could be a number of things including bad equipment in the telco office.
http://www.sandman.com/files/teldiagchart.pdf

battery x'ed ring?