These calls (always appearing as "PPC" on the call display) come from numbers that fit the following number profile: 613-288-0xxx. Single, intermittent tones (similar to those of a fax trying to initiate a response) are all you hear, and if you have an answering machine the device that is calling your number will leave a message with that annoying tone. Extremely irritating, since there are 1000 different numbers this call could be coming from, therefore you cannot block the offending numbers!