Speakers make hissing sound

Installed a RF 4 channel amp for Front and Rears. Sound was great and much improved than using the HU. A few weeks later I decided to add a powered sub. The Rockford amp has a pass-thru for RCAs. So I connected a set of RCAs to the pass-thru port and connected the other end to the powered sub. I get a hissing noise from the speakers (not the sub) as soon as I turn the power on.

The sound does not increase with RPMs and goes away when amp is disconnected from power. All grounds are bolted to sanded portions of the frame. Any ideas? Thanks!

 

check ground, or find a better ground. I have the same issue with a stock head unit, aftermarket speakers and amp. I had to turn the gain down a bit, still hisses but not as bad.

 

What HU?
What RF amp?
What powered sub?
What RCA cables?
How did you set sensitivity?
Did you reset sensitivity after connecting the powered sub?

 

Gains were set after amp was installed using the CLEAN steps in the Rockford Manual. Gains have not been adjusted after hooking up the powered sub.

Sony XAV-AX100 HU
https://www.crutchfield.com/p_158XAV100/Sony-XAV-AX100.html

Rockford Fosgate R2-500X4 Amp
https://www.crutchfield.com/p_575R2500X4/Rockford-Fosgate-R2-500X4.html

Sound Ordnance B-8PTD Powered Sub
https://www.crutchfield.com/p_777B8PTD/Sound-Ordnance-B-8PTD.html

EFX Marine RCA Patch Cables
https://www.crutchfield.com/p_142R12/EFX-Marine-RCA-Patch-Cables-12-foot.html

 

I noticed the Sony is 5 channel out, and the powered sub has L/R Sub in, but the amplifier only has front and rear inputs, which is fine I suppose but it seems like the pass through, when used causes a change in the input and something gets angry.

It’s either a shitty design or something is wrong so what I would do is reset the sensitivity with everything hooked up and if there is no change, run directly from your stereo’s subwoofer out to the powered subwoofer. You may need to use a splitter, some sub amps require both L/R connections for eliminating noise in the signal. A side benefit is you will gain some control of your sub level from the stereo.

 

Thank you for looking into this, I've been losing my mind! I checked all RCA connections and zeroed out the amp settings and started from scratch. The hiss is 95% gone.....which is fine with me! Gains were initially both set to around 7. After resetting everything they're both hovering around 3. Thank you for your help!

 

Good to hear man, any time.

 

I would re-do the grounds for the amps ...