Replacing PCM - aftermarket headunit-Very noisy+weird noises

[uk996]

I know there are plenty of threads on this subject already.
I have a 2002 996 which has factory Bose and original navigation, PCM with a telephone handset. (non-MOST)

I asked the garage to replace it with an Alpine ILX700. They did a bit of a hatchet job, wired the speaker out into the Bose and didn't connect any power to the aerial amp, so radio reception was pretty bad.

I ended up stripping it all out and working out how to wire in the preouts etc. Did all that and got it working ish. Problem is that it sounds awful. There is lots of interference type noises which is very noticeable. I've wired the HU into my stereo to eliminate that, it was nice and clean, no problems at all.

So it's likely to be incompatibility between the HU and the Bose system. Perhaps ground loops.

However I don't recall reading how people have solved the issue.
What did you guys do?

• Live with it?
  Put the original back in?
  Ripped out the Bose?

I'm not after concert hall, super-fi, the 996 is way too noisy for that, just something simple, nice and clean with BT music streaming and BT phone.

I may even go single DIN, like the Continental unit for 1990s looking simplicity.

 

[uk996]

Any solve the noise problem?

 

[Dammit]

What seemed to be good for mine was to ground the head unit to its own location on the chassis, rather than sharing an earth with the dash.

Night and day difference to reception.

 

[uk996]

Good idea, I'll try that. Dammit are you a MB fan too?

 

[uk996]

Update
Changing the earthing point didn't make any difference.
Still got the noises, like an old GSM phone communicating with the base station.

Solution, rather drastic, but I sold the Alpine and bought a more modern JVC KW-M745DBT with DAB+, CarPlay and Autoplay for not many notes, £270 for a refurbished unit.

No more funny noises. The only down side is that I can't change the start up screen, minor annoyance.

The sound quality is still a bit MEH. It isn't the HU, it's the rest of the system. I suspect the Bose amp and or speakers. Since I have a few amps not doing anything, I'll see if the amp makes a significant improvement.

I find the SQ is a little muffled and the mid-bass is boomy and single note.
I've read that the Bose sub is two 2ohm 5" speaker wired in parallel in a ported cabinet.
- Is it worth rewiring and changing the speakers?
- Anyone fitted 6.5/8" subs?

Just to add, I'm not after decent SQ, the 996 is way too noisy for that.