2003 mach stereo has low volume
 

Hello,
I just got a 2003 mustang with the Mach audio system.
The radio plays and operates ok, but there is NO real volume. As though the amps are not working?!?
I checked the mini fuses under hood, and the fuse under dash, and all are not burnt. they look fine.
Please help me find my volume.
Thanks,
Bo