Thanks for info! Unfortunately I have a bit different harness and could not copy that.. Could you measure the voltage level now turning your amp on? Just thinking could I just reduce the voltage level to achieve what you have. At the moment I have 10.8V switching the amp on.!!!!!HISSING SOLVED!!!!!
So, because this was my first time with replacing a head unit, I made some uninformed mistakes. Unfortunately there are no instructions for car specific model installations so it required some research. BUT I hope this post can be used to help others down the line. For anyone using a Teyes CC3 and using the OEM Bose amp from the 2013 CX-5 car, make sure you do the following, a little history of my process is also included:
The unit was shipped and received with two Power harnesses. One harness had a blue cable labelled "AMP-C" while the other harness had the blue wire labelled "AMP" and ALOT more connections like RCA etc. The harness with the AMP-C wire also had the Antenna assembly photo'd below with no RCA connectors:
View attachment 5922199
What caused the hiss was using this harness originally, attaching the AMP-C on this harness to the AMP-C on the audio interface harness photo'd below:
View attachment 5922201
This was a mistake. the amp was receiving power and signal through the AMP-C connection i soldered giving the amp more power than it could deal with essentially feeding the amp a line level signal hence the hissing.
So after much troubleshooting, i noticed that the other harness that had the blue "AMP" wire had a number of RCA inputs (RCA are normally passive signal)! And I had a spare RCA harness that came with the unit (also photo'd above next to the audio interface harness)!
Once I soldered the AMP-C from the audio interface harness to the power harness's AMP wire, I plugged in the RCA cable harness to the power harness as well(FR, FL, RR, RL). The RCA harness plugs into the back of the CC3. Photo below:
View attachment 5922219
Now came the ANT car connection, the power harness with the RCA Plugs and "AMP" wire did not come with this, so I had to cut the blue connector (marked with an "X" in the photo above) from this harness and solder it to the ANT lead on the other. See photo above and below^^^
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Once everything was assembled into the car, it worked. It just worked. I was able to bring power conditioning in the CC3 all the way back up to 60 and it sounds crystal clear.