Why Car makes intermittent shuddering sound which goes away when I step on brake on 1990 Saab 900

Problem happens within 10-20minutes of driving.Becomes a high pitch on freeway then a slower shuddering sound on city block streets. When I step on brake sound goes away instantly and completely for a few minutes then reappears.At first sounds like passenger side by wheels then sounds more like center of car under the dashboard.

by in San Francisco, CA on August 04, 2012
1 answer 2 comments
ANSWER by on August 04, 2012
Check brakes , may be 'wear indicators' on brake pads hitting rotors (sound similar to fingernails on a chalk board)
COMMENT by on August 09, 2012
Took car today to Midas for brake checkup and test drive.Manager took test drive and heard the sound and how it went away upon stepping on brake.Midas technician will look at right brakes tomorrow as he says there is a high probability it is the brake pads and/or warped rotor.Thanks for the excellent advice.Will know better after the brake repairs have been completed and car goes on another test drive.Midas changed brake pads and rotors and so far intermittent shuddering sound has not returned on test drive..Only the next workweek of driving will tell for sure.Thank you.
COMMENT by on August 12, 2012
Thank you for the feedback. It's the only way I have of knowing if I've been any help!