Engine Noise

Hey all, I am having some engine Noise coming through my door speakers. I've tried adding a ground wire to the amp, moving the ground, added 2 ground loop isolators (one for each pair of door speakers), cleaning up the wiring harness mess that the installer created, bought a brand new rca cable (high end ones) and nothing helped. I've got a boss 3700w 5ch amp, 2x12in infinity reference 1262w,2x4 way boss 6.5 inch speakers in the front doors,2x3 way kicker 6.5 inch speakers in rear doors, Sony mex-5100bh stereo. Everything sounds great, responsive bass, crisp highs, lights don't dim, but when there is no music playing or I'm listening to an audiobook there is engine noise. Does anyone have suggestions on what this may be? I don't want to send my radio back unless it's 100% the cause. It's there any way I can test if the radio rca is faulty? O this is in a hyundai elantra 2013 gls no navigation system.

If you turn all of the gain controls on the amp all the way down, does the noise go away?

Try adding a ground from the back of the radio to chassis ground, then to amp if that doesn't help.

Otherwise everything you have done won't help if it is coming into the the signal through the amp. You checked that the amp ground is good and made sure you have a large enough ground wire for it. Otherwise you have some leaky components inside the amp that are letting in noise through its power supply.