Constant humming noise with RNS on

[HPsauce]

Bit of a weird one this. I have noticed it before so I think it's been there a long time......
Basically with the RNS-C (+Bose) switched on there's a constant background hum.
I noticed it again today as I was in the car to program some "waypoints" into the SatNav so nothing was else switched on, no key in the ignition.

The volume is constant and doesn't vary with ANY of the audio controls (volume, balance, fade, whatever).
When driving you don't notice it due to other background noises.

Just wondered if anyone else had this, knew what it was and if it's a concern?

[PsYcHe]

do you have a bluetooth unit close to the RNS?

[47p2]

Could it be a cooling fan?

[HPsauce]

Definitely NOT a fan or anything else like that; it comes out of the speakers and NOTHING is on apart from the RNS - and it goes when RNS is switched off.
No bluetooth, though I do have a factory handsfree phone installed - handset was not there. Something to test...

[HPsauce]

Hmmm, just tested with the phone handset in place.
Hum is still there, on all inputs (Radio, CD, TV, Aux) and at all volume settings, BUT when I make a phone call and it switches to the phone audio (e.g. ringing out) the hum goes.

I don't know much about how that works though, I'm sure I read somewhere that there's a separate speaker for the phone in the drivers door and when activated the main speakers are cut off.
That "suggests" it's possibly something to do with the (Bose) amplification to the main speakers.

[david@a8parts]

Couple of thoughts:

Have you had a look at the BOSE amp and connector? We had a customer with a similar interference problem a couple of months back and water had found its way into the well where the Amp sits (beneath the CD changer) and most of the wires on the Bose amp connector were corroded and nasty looking. They were all still in tact and connected but in poor shape - he patched in a good connector with a foot or so of wire to eliminate any of his old corroded copper and his problem was fixed.

Another thing I would check is on the back of the head unit itself there is a spade connector for an earth wire - this sometimes gets left off and can also cause an annoying interferency type problem.

[HPsauce]

Thanks David,
I'm pretty sure it's all fine around the Amp itself as I was looking in there not long ago to see where to connect in a DVB-T tuner (not yet started on that), but I'll check again.

As for the earthing on the head unit, that's obviously worth checking. Presumably it has to come out? I have the very late PF RNS-C which is rectangular and have absolutely no idea how to pull it out - is there a write-up somewhere?

[daviesbike]

there is a a guide somewhere if i remember but it is simple you need 4 keys to take it out,
you can buy them off ebay for a couple of quid http://www.ebay.co.uk/itm/CT22AU01-A...#ht_2126wt_932


you need 4 to be honest

i had the same problem and it was the earth cable on the back of the unit the way to see if it is the earth without removal is start the car switch to AV on the tv and turn the volume up on the stereo and go for a drive take it through the revs and it it makes a supercharger kind of noise then that is due to the earth on the back of the RNS-C
i plugged it back in and snipped the Gala feed while i was there to get TV in motion

you can just go to halfords and ask them kindly to pop the keys in for you they were more than happy to do it for me

[HPsauce]

Originally Posted by daviesbike

it is simple you need 4 keys to take it out

Ah, I see. Didn't spot the holes at first, they're very thin and far from obvious!

[Adrian E]

You'll know the keys are in the right way round when you can't get them out again! They will click into place and you use the rings on the keys to ease the unit out

To release the keys, push the sprung tabs the keys are engaged in on the sides of the unit and the keys will release. Don't try just tugging them out!

Mine comes out very easily