I am at my wits end trying to solve system noise issues. I am dealing with 3 separate problems that all cropped up at the same time. I have a new alternator whine, a low rumbling static like sound, and system hiss that all cropped up when I installed a DSP into my system.
Background:
I received a Dayton DSP-408 for my birthday last week. Got it installed 5 days ago and have been chasing noise ever since.
my old setup that was noise free was a older pioneer hu into a PG tantrum 600.4 with two channels feeding front passives and two channels bridged to my sub. Being a single amp system I had the power and ground wires direct to the amp, no distribution blocks needed.
My new setup is Hu to DSP-408 using the same 2 pairs of rca cables that i already had in place. from the dsp I have 2 new short rcas to the old PG amp. added a third set to a MTX thunder ta202 to power my tweeters. I re used the same power and ground cables by running them into distribution blocks and than ran new power and ground wires from there to both amps plus the dsp.
after installing I keyed on the system and I immediately noticed a system hiss and a low rumble sound coming from my door woofers and my sub. after lowering the main volume on the dsp I got the hiss to a manageable level and after some experimenting I found that the rumble only occurs when I have my HU set to disc. it does not make the noise when using the tuner or aux input. I initially thought it was no big deal because I use my aux in 90% of the time.
After finishing a basic set up of the DSP i finally started the engine and than I was greeted by a very loud whining noise. as a temporary band-aid I was able to lower the main volume on the dsp another 20 points to get it to the point of minor annoyance as opposed to piercingly shrill.
Things that I have tried to isolate or eliminate the noise:
I replaced the factory ground cable from the battery to the chassis with a much larger wire. no change.
Ran a new dedicated ground from the battery to the HU. Made the noise worse.
ran a temporary connection from the oem radio ground wire the the HU chassis. The noise got slightly better.
Removed the oem ground and the direct to battery ground and installed a ground wire from the HU to my distribution block so everything in the system has a common ground. noise is the same as it was running the oem radio ground but better than it was running a ground wire direct to the battery.
tried testing the system with the HU out of the dash and resting on my knee. no change.
I tried disconnecting the rcas from the back of the HU to see if I was picking up noise in the cables. with the system powered up and the rcas connected to the dsp but not the HU my alternator whine is gone but my noise floor hiss is still present.
Tried swapping to an old Kenwood HU that I had sitting around. Noise is unchanged.
I double checked and freshly sanded my ground point in the trunk to see if that would help. No change to the noise.
The last thing I can think of to try is looking for a different part of the chassis to ground my distribution block which I am going to attempt later today.
If that fails than the only other things I can think of would be to add some dedicated ground cables for the alternator housing and the engine block to see if somehow i have a week factory ground causing an issue underhood, pulling a A/C ripple wave form on the charging system under load, or ordering a set of ground loop isolators like these https://www.crutchfield.com/p_127SNI1/PAC-SNI-1.html
now that I have a taste of what a fully active system can do I do not want to go back to passives again but these noise problems are killing me.
Any tips or suggestions would be very appreciated.