My first stop for any MINI trouble is this forum and after trying several things, living with the problem for months and finally solving it today, I thought I would share so someone else can avoid the hassles I had.

PROBLEM: Feedback in the speakers causing a hissing sound, matching the engine revs (no hiss with the engine off, more hiss with the engine revving, especially when down-shifting).

SOLUTION: Ground loop isolators plugged directly into my receiver's RCA out jacks. Hissing is gone.

I have read many threads both on this forum and others, as well as going through Crutchfield's troubleshooting guide. Nothing seemed to work for me, though I suspect the problem was known all along -- difference in ground potential causing the feedback and hissing (or in other words, I was not grounded as well as I needed to be).

A little background on my system ... other than some wiring, nothing is stock now, but nothing that I have probably counts for high end. I have an R52 S that I use to commute back and forth to work with the top down as much as possible every day. At speed on the motorway with the top down, the stock system was simply not loud enough (loads of wind noise), so that is where my quest to improve began. However, I also wanted to keep the stock-look as much as possible. Here are my components:

• Kenwood KDC X995 CD Receiver (I went with this a few years ago because it had the audio (HD radio, pre-amp & sub outputs, DSP, onboard amp (initially no external amp), range, etc.) and convenience (steering wheel compatible, iPod/iPhone, Parrot microphone, etc.) as well as having a variable display color so I could match (at least get close) the stock orange lighting)
• PAC SWI-JACK (to connect the receiver to the stock steering wheel controls)
• Polk Audio DXi6500 component speakers (front 6.5" + tweeter)
• Polk Audio DXi525 coaxial speakers (rear 5.25")
• Sound Ordnance B-8PTD (powered 8" subwoofer that sits under the drivers' seat to make sure I can feel the thumps)
• Clarion XC1410 amplifier (4-channel 300 amp, mounted under the passenger seat)

I first ran for about two years with the receiver and steering control. Then I added in the speakers and the subwoofer. The hissing started when I added in the amplifier, which was run with two pair of RCA cables from the receiver into the amplifier.

It seemed to me that the noise got worse with time, but it also started to get colder, which meant top up and less wind noise (so perhaps the change was simply in my mind).

My first attempt to resolve the problem was to improve the ground connection for the new amplifier. My amplifier is small and is zip-tied to the steel webbing of the passenger seat (which also means it will not get directly blasted with hot air from the heater going to back passengers). I ran a lead directly from the positive battery terminal in the rear and the ground cable to one of the front seat track bolts (which bolt into the frame). I thought there was a chance this connection was not on as much bare metal as it could be, so I used a Dremel tool with a wire brush to clear away the floor treatment and make sure my ground lead was touching bare metal.

No improvement.

My second attempt was to improve the grounding overall by running a lead from the rear negative battery terminal directly to the amplifier. To eliminate any chance of a potential difference, I also spliced in a lead from the receiver ground and decided to connect up the subwoofer as well for good measure at the same time. The wiring is not difficult, but removing seats and interior body parts made this job time consuming. By removing the chance for a potential difference (grounding the receiver to the same line that was grounding the amplifier), I thought the problem would certainly be solved.

No improvement.

At this point, I was at a loss as to what to try next and was considering just "living with it". I read from this forum that some people had tried capacitors and successfully removed the noise, and while this did not seem to make sense as a way to solve my problem, I was considering it as I could see no other options.

Then I came across the ground loop isolator option. I went with PAC SNI-1 from Amazon.com for $7.46 each (needed two). The other option I saw was Boss Audio B25N and Raptor GL15. They all cost about the same and I suspect that any of them would work. I am not as big a fan of Boss, so I eliminated that option and was leaning towards Raptor, but saw that the PAC product also gave a 1.3 dB gain, so I went with it (again, wind noise is fierce at 90 MPH).

Installation is plug-and-play. In fact, the space directly behind the receiver is fairly cramped and the three sets of RCA cables coming in was problematic in getting the receiver to fit as it was. The PAC SNI-1 actually gave me a slightly thinner and more flexible RCA plug into the receiver and the extra line to box that is part of the isolator allowed me to push my thicker RCA cables going to the amplifier further out of the way (meaning the receiver fit better). I realize that thicker cables usually mean more insulation and potentially better sound, but I can not hear the difference myself and the better fitting receiver is a better option for me (bumpy California motorways).

TAKE AWAY: For anyone else with speaker noise, especially after installing an amplifier with RCA leads coming in, consider ground loop isolators to solve your problem. In fact, anyone planning to install an amplifier should consider these from the start.

Happy motoring!

 

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