I have had trouble with this problem for quite some time. Everytime I press the brakes there is a grinding in the left rear brake. I only hear it when i press the brake pedal and it is only from left rear side. I have replaced the rotor, caliper, and pad but nothing seems to help. Does anyone have any suggestions on what else to do. Any input would be great.. Thanks

Here is something that you can cet from the dealer. The Service Bulletin that GM prepared to help dealers with this issue is listed below

Rear Brake Moan/Groan During Brake Apply (Replace Rear Brake Pads #99-05-23-003 - (03/12/1999)
1998-99 Buick Regal

1998-99 Oldsmobile Intrigue

1998-99 Pontiac Grand Prix

Condition
Some customers may comment on a moan/groan type noise coming from the rear of the vehicle that is heard in the vehicle's passenger compartment. This condition is most apparent during moderate brake apply; when the vehicle is slowing or approaching a stop and typically does not occur on a brand new vehicle.

Cause
This noise may be generated at the rear brake pad/brake rotor interface during a brake application, which is transmitted into the vehicle's underbody through the rear suspension components.

Correction
Replace the existing rear disc brake pads with P/N 18023377, following the service procedure in the Disc Brakes sub-section of the Service Manual.


Important
When the new pads are installed, the burnishing procedure indicated below, MUST be performed in place of the procedure described in the Service Manual. Proper burnishing is essential to insure elimination of this moan/groan noise.


Burnishing Procedure
Make four stops from 50 mph (80 km) with heavy/aggressive pedal apply, followed by four stops from 30 mph (48 km) with medium/moderate pedal apply. Do not overheat the brakes.

Parts Information
Part Number
Description

18023377
Rear Disc Brake Pad Kit


Parts are currently available from GMSPO (the dealer).

Thanks a lot for the information. THis sounds exactly like what my brakes are doing.. THis has been a pesky problem for quite some time and i will try this and see if it helps...