2002 S3 (8L) Bose speakers here, Swapped the Chorus II tape deck for an Alpine UTE-72BT and went with the PC9-410 harness (as the HU has RCA pre-outs). Managed to get everything working well except for a one thing... At any volume above 0 on the HU, there is a noticeable hiss coming from all the speakers. Whilst driving around it's inaudible over the road/engine noise, but it's pretty annoying for quiet listening. I'm not using the high-to-low signal converter cable so that can't be the issue. Any ideas on what I could do?