Need Help... Aftermarket Speaker/Amp Install

After I replaced all the stock speakers and installed an amp, I am hearing a hissing / white noise sound whenever I turned on the car. Any help would be greatly appreciated

About the car:
- 2013 Prius III (non JBL)
- Stock HU
- 2 Front Speakers are old / 2 Rear Speakers are new
- Amplifier is new (Pioneer GM-D9605) GM-D9605 - Class D 5-Channel Amplifier with Wired Bass Boost Remote | Pioneer Electronics USA
- Using PAC SNI-35 Line Out Converter (LOC) to connect amp to stock HU
- Ran new speaker wire from speaker locations to amp, used LOC to run RCAs from HU to amp

About the problem:
- White noise / hissing when starting up the car
- Noise is coming from all speakers

Things I have tried:
- Noise is the same while playing from Radio / Bluetooth / USB connection
- Noise is the same when the audio is turned OFF
- Connected to Speaker Level Input on the amp. The amp comes with speaker level input wires that I could use to connect directly to the amp instead of using the LOC. Using the amp Speaker Level Input did NOT fix the issue.
- Testing ground connection of amp. I tested the ground wire for the amp with a voltage meter by measuring the resistance. I set my voltage meter to 200 OHM scale and the reading I got from the amp ground to battery ground was between 0.2 - 0.3 OHMS
- Testing ground connection for HU. I received the same reading as above

Im not sure where what to check next. I really prefer to keep the stock HU (mostly because I dont have the money to upgrade yet )

 

I disconnected the RCAs from the amp and the noise reduced a good amount (not completely gone), then I reconnected the RCAs to the amp, and disconnected the RCA from the LOC near the HU, the noise didnt improve at all. So I am going to try a ground loop noise isolator (PAC SNI-1)

 

Tried turning down the gain on the amp and LOC, the only time the noise was gone is when the gain was all the way down

Thanks