rattling noise when A/C on and foot on brake while in gear

It's your serpentine belt. The way the belt twists and turns on a Suzuki is crazy. I have to replace mine every 2yrs but they only cost $20. It's the taking apart half the car that's the worst. You have to go through the wheel/axle area.

belts don't rattle.... turning the a/c on or off will cause a change in the engine's rpm..... putting the car in neutral will cause a change in the engines rpm.... a loose and/or broken heat shield on the vehicles exhaust is rattling.if its on the pipe........ just take it off. if it is one of the heat shields connected to the bottom of the car..... replace it. If the exhaust is mounted too close to the bottom of the car without a heat shield present the carpet on the inside of the car will get hot and could possibly catch fire.

i've had the same problem. replaced belt but same persisted. removed belt and manually engage a/c clutch and found a/c compressor heavy to turn over. replaced tensioner pulley cost $250 cdn. no more rattling for now . i'll have to find out why copressor not turning over easy some time soon before the load on tensioner scews up bearing again.