I have a 2000 GTP and thanks to this thread I have found the problem solver here. My car has been to a couple different dealerships with no luck. Thanks to vt102 my problem is solved!!!

There were two of the brake lines that were going into the pump and they were touching each other causing this horrible buzzing noise ( just the same as described above) My husband took about 10 minutes in the garage repositioning them and that was the problem. Thanks again VT102!!!!
Gina