I have received numerous calls from this number this morning (three before I left for work - there may hve been other calls in the meantime) plus one call in the evening. Every time this number calls, the phone (land line) does not recover its normal dial tone. Instead, it has an intermittent tone, different than the "Busy" tone. When I called it back, it sounded like a modem/fax. Could it be a hacker of some sort?