speakers/amps sound fine until i turn my car's engine on

then only the rear speakres produce sound

and i think the front speakers produce a cannoot hear sound that makes my
ears hurt, a sound tha tis below 20 db


i have one set headunit ,rca cables run on the right side of car, amp
power cable runs on the left side. the amp's ground cable has a isolated
grounding point away from any other grounding points.

the has a 15 amp fuse and so does the fuse holder near the battery


the amp is suppose to be new i bought it off ebay from an audio dealer
it came with new packages and amnuals