Static Noise coming from rear deck speakers, 07 S60

[tsteph99]

I have been scouring the internet trying to find a solution to this and as someone who is not super familiar with cars I don't want to try something and mess it up. I have a 2007 S60 and as of about 2 months ago the rear deck speakers have a constant static even when the radio is turned off and the sound quality has gone way down. I know they're not blown because when the engine isn't on and the key is in the first or second slot the speakers sound great, and every once in a while when I'm driving the speakers will work normally for a minute or two and then go back to being bad. Any help/suggestions would be greatly appreciated! Also the problem started after a week or two of sub zero temperatures and that may have something to do with it but I'm not sure.

Thanks!

[EngineeringBloke]

The rear deck speakers are in parallel with the rear door speakers, so both get the same electrical signal. You should be hearing the same sound/noise from both of those.

The static continuing when the radio is off suggests you have a problem with the audio amplifier. However, these usually get a turn on signal only when the head unit is on, so your situation is odd.

This could be an amplifier power supply capacitor in the process of failing, but this would typically also affect the front channels, too.

Before the engine is started, the system is running with about 12v, after, the alternator provides 14v or so, and the increased voltage may have an effect. Also there may be some interference from the engine when running, but this is not a problem for most unmodified cars.

What is your head unit model number?
Do you have an amplifier under the front passenger seat?

[oragex]

Which head unit is this? The HU-8xx ones are known to fail, and they also have an amp under front pass seat that gets corroded from winter snow/salt. The radio and amp are pretty easily swapped out (car battery disconnect is mandatory) with a used unit off Ebay from the same year for the head unit, any year for the amp

[EngineeringBloke]

I think there are different amplifiers - a 200 watt and a 300 watt model, as I recall.

[tsteph99]

It is the HU-650 and from the research I've done I don't think I have an amplifier under the passenger seat but I haven't physically checked.
Thanks again