Only one sub preout......how to hook up(noise)

[eyeopeningepisode]

Thanks in advance to any help offered. Here is the issue.

My head unit only has one rca for subwoofer preout. I have seen some head units with SWL and SWR distinguishing on them.

My head unit only has one which is labeled subwoofer1. Here is the deal....i run rcas from my monoblock amp to the headunit

But then i have a y splitter adapter so it receives the rca from amp and goes into my one sub preout. This sounds extremely nice and loud.

However in this setup..if i put the blinkers i can hear the subs thumping a bit when nomusic is playing. If i raise up the windows...or dow....i hear the thump

Through the subs again. If i stop at a drive thru..to order food....i turn off the trucks in cities Diesel and they can't hear me, and when I started back up again I can hear the subs thump.

If I go back to the Y adapter and disconnect one of the RCA's coming from the amplifier then the thumps will go away however the system is nowhere near as loud.

Any ideas? I have good ground going to the truck chasis. I am thinking upgrading head units but I want to get this one working.

[Wasteland_Audio]

The sound drops because the amp only receives half the signal voltage when only plugged in on one channel. The feedback however is a grounding and possibly a signal interference issue. Make sure to run the rca cable as far away from any 12 volt wires as possible. If that doesn't work, you may have a problem with the internal circuitry of the head unit itself. In my experience you would be much better off getting a new deck with a dedicated pair of sub-out channels. The signal will be clearer and you will get a lot less interference.