When I read this type of post I think one thing
Ground your radio with one Black wire ground - meaning...
Open up the case...
Locate Black Ground wire...
That wire - unsolder it from the board...tape it off
In same hole - solder wire from Hole to CASE - your back panel - scratch/scrape or file off a spot (or drill and bolt/lug combo a wire to back/Rear metal panel - to bare metal and if needed a small torch (for heat to take solder to panel) and solder wire from Case to Board Ground - this can help you remove the ground loop even further. For when you solder or bolt the ground of the NEGATIVE Board Ground wire to the CASE - now CASE, COAX shield and board ground are all the SAME you've "strapped your Radio grounds together".
So how does the radio get power?
From the ability of the Coax SHIELD - being connected to the Amp and To the Antenna - they also provide grounding points - your noise is due to the inductive event of ground loop noise loop - your systems' grounds are not all equal - the radio tells you this in it's noise level.
So if the Noise level is still too high or If it don't work for reducing noise, you can detach the case to board jumper wire and resolder your black wire in-- as in - reconnect/resolder the black wire to your ground hole inside the radio - but then you will have the noise level of this setup all the time.
BUT! - if this reduces your noise, then leave wire taped off, or remove, cut or just disconnect Black wire KEEP ORANGE wire if your radio is equipped with 3-wire...Black is no longer used for ground ok? Best to get rid of it or just tape off...
The Reason why this comes up is because on some radios like the Cobra 18 RV/WX and such - those Cobra 18's They used 3 wire power hookup - so one, Orange, wire went to Battery, while the other, RED (the bigger fused wire too) went to switched. BUT BLACK wire? Some Cobra 18's didn't need the Black wire if you mounted it - you could just leave it open free and never use it or clip it off because the radio was NEGATIVE ground only - MEANING it's CASE was Grounded to the Same Black Wire ground - and if permanently mounted, your bracket and or coax did the ground for you.
The 18 - at least some, came with Memory and DW or Dual Watch along with WX monitor - so the ORANGE wire needed to go somewhere with constant supply to power it - for if you didn't the Red wire remains to SWITCHED but if they wanted WX they couldn't hear any Alerts that may come thru and the Radio won't power up. Orange provided the power for WX monitor and Radio Battery memory (keep alive) so - the Alarm would sound and you could then use WX but not CB - you needed Red wire to do that.
What do people normally have? 2 Wire plug, if they lost the original - so the radio wouldn't power up so a lot of times I grounded the Case to Hole_That_Black_Wire_Went inside - used a jumper from RED inside to ORANGE hole inside to wire memory to go to their battery to keep the WX function and Memory alive - in doing this they found the radio did a lot better permanently mounted and noises and RF problems were a LOT less.
Also inclusive you may have the Radio that is only Negative Ground only radio polarity so you have at least 3 different types of grounding issues,
Uniden 3-pin plug/Jack needing 3 wire, Orange Battery but Red to Switched or TIE both together
Grommet'ed - 2-wire -RED to Battery (constant) Black to Frame or Battery Negative
No ground at CASE of radio (between the Seats - uses Cigarette lighter or LONG WIRE run for Ground)
- MAN! Just skip this type of install AVOID LIKE THE COVID-19 IF YOU CAN
So for best results - if you aren't living in Australia or other countries that have the vehicles Positively Grounded versus the standard American SAE Negative Ground - Best to GROUND to Radio BACK panel and let the Coax Shield provide the Ground for you - at the amp or at the antenna.
