DYI AUX cable install - Getting engine interference though

[VAGslag]

I did a DIY AUX cable install in my 2001 Audi A3 by basically tricking the OE head unit into thinking the AUX cable is what my CD player (in boot) is playing. It works but when using it I get interference from the engine through the speakers.

There's basically a short phono cable coming out the back of the HU and then a phono to jack going into the car. To try combat the interference I installed a ground loop isolator in between (similar to link at bottom), which has helped but still get a fair bit of interference.

One thing that may be relevant... I wanted the jack in the arm rest, so to avoid drilling any large holes in the arm rest I snipped the cable, fed it through a small hole and then spliced it back together further down. Not sure if this could mess with any shielding or something? . . Not something I'm an expert on to be honest!

Any thoughts on this? Electrics really isn't my strong point! Thanks

http://www.ebay.co.uk/itm/PRO-DJ-GOLD-RCA-PHONO-GR...

[VAGslag]

No one? . . Thought someone would have a good idea!?

[jasonh77]

Most likely you've interfered with the shielding a little bit..

Easy way to check is with a new cable plugged in and tested lying loose - that way you're checking it with an unmolested cable?