Not just with this Bonneville but with both of them, and not just with this head unit but with one or two others, I've had whirring that sounds like the alternator'* noise is being heard through the speakers. I did once take care of it by cranking down the amps to absolutely no gain, but then I couldn't hear much and the music I did hear was weak.

I have a Pioneer head unit, relatively modern but with a model number I'll check soon, and it'* grounded with an 8 gauge wire straight to the chassis. This helped cut back on the noise.

The Pioneer head unit goes to an Infinity Reference 4-channel amp that powers two sets of component speakers in all four door panels plus two rear deck speakers (4 x 6.5, 4 x 3/4 + 2 x 6x9), and the rear 6x9 speakers were added after everything was already set up and had been buzzing.

Also, there'* a 2-channel sub amp that powers two woofers, but that was also added later. The whirring existed with just the Infinity amp going to four component speakers, one per channel.

The amps are grounded to sanded-down spots in the trunk, and all the connections are fresh and tight. The only thing I may have left is that the power for the amplifiers comes from the fuse panel with the dual power wires attaching where the alternator hooks up. I put a 4 gauge wire from the alternator straight to the fuse panel. I would like to extend the amps' wires to the battery, but there'* not much room on the side-posts. Since the battery is dying, I'm going to get a dual post, probably an Optima, and I'll see what happens.

Ultimately, could the last thing to change be swapping the power lines to go to the battery? Is that essentially what'* causing this, do you think, or is there more that can be done? I've tried ground loop isolators, RCA line filters, etc., but those only made the problem worse or maintained it.

Are both of the decks Pioneer? I would try grounding your rca'* to the deck, Pioneer is notorious for this problem. It'* free to do and worth a shot, let me know how this works out.

Ive never heard of Pioneer having this problem. All i use is Pioneer HU'*.

I've never had this problem with aftermarket HU'* or speakers. The only time I've ever got this sound was while running a CB radio, then I would hear the whir in the CB.

Yes, both head units were Pioneer models. I'm about to go drive the SLO, so I'll let you know the model number exactly. You're saying I should wrap the ground from the RCA and attach that to the head unit? I'll give that a shot hopefully tomorrow.

Sorry about announcing this problem so broadly. I'm sure that Pioneer is an awesome brand, and as you see, I've had two head units from them so far. They're pretty awesome, but it'* just too bad about the background noise.

I wont use anything other than Pioneer HU'*. So much adjustability! more than most people will need or use but its in there

I've considered Kenwood and Alpine head units as well. But Pioneer always wins when I choose a new one. I've helped two other friends choose Pioneer, and not only are they completely satisfied, but they don't have that whirring!

I never had a whir with my Pioneer in my 91 S10. I've only had Kenwood since then. Something somewhere isn't grounded properly. That'* what is causing this.

I'm willing to blame grounds, but I can't find much. The amps are grounded by-the-book, and the head unit has a huge wire that quickly goes to a common chassis ground.

Maybe one thing that can help is that when I hit the brakes, there'* a slight pop. Where do the brake lights contact ground?

do u have a chaffed or untaped wire grounding out?