Weird sounds, need help please

Technical Area Electrics & ICE
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  1. My model of MX-5 is: Mk3.5 PRHT
  2. I’m based near: Colwyn Bay
  3. I’m looking for technical help or recommendations on: Ok, I have a really odd issue. When I start my car there is an intermittent pop or clunk which sounds like someone is rapping the car body with a knuckle. It does it whether moving or not, roof up or down, in gear or neutral. Every time this happens the radio cuts out for around 1.5 seconds which is why I put it in the electrical section. I cannot locate the source of the noise. My 6 month old battery is discharging quite quickly in case that’s relevant though I haven’t been able to drive far for a while. Any ideas or qualifying questions? Thanks.
2

Check your starter motor. Sounds like it is taking high current which is killing the radio.

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Would that make loud pop / knock sounds? These sound like they come from the back of the car somewhere. It’s happening when the engine is running but not when starting.

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A long shot but do you have your aircon running? If so, try turning it off.

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Thanks, no - aircon is off.

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Any damp in passenger side footwell? Weird stuff happens when scuttle grommets goes.

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You have a BOSE radio in your car? It’s the amplifier mounted behind the seats which is on its way out is my guess. Happened to me, I ended up disconnecting it and putting an aftermarket head unit in, bypassing it completely. There is a company in Edinburgh that specialises in repairs to these, I can’t remember their name though.

Found it,

Barrie

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Thanks Barrie, I think you nailed it. Could you please tell me how to disconnect it safely or point me to a resource? Firstly where it is / which plastics to remove then which wires to pull / cut. Thanks so much for your contribution, I thought the haunted car sounds could potentially be coming through the speakers though they do sound somewhat mechanical.

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Also, since I suspect the Bose is what’s draining my battery, which fuses can I pull to disable the whole radio / amp? Presumably I can do that without disabling some essential car functionality?

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Hi Phil, the amp is behind a square plastic cover, situated behind the drivers seat. A trim tool or similar thing will prise out the cover, exposing the amp. On yours, there are 3 plugs on the amp to disconnect from the main loom. You should be able to do that with the amp in situ. If not, there are a few small torx bolts holding it in. Once removed/disabled, obviously you will not have any functionality from the head unit but that’s all. Be mindful, if you are considering a 2nd hand replacement that yours is a 3 plug amp, earlier ones are 2 plug and not compatible. The company I linked to would be your best bet if retaining the OEM Bose set up. Alternatively, I by passed the amp and installed an aftermarket unit. This though will end up costing more as you need a new fascia, new headunit of your choice, wiring harness adapter, steering wheel control patch lead, different speakers also, as the Bose ones are different impedance and won’t work without their amp.
Barrie

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Thanks Barrie, trim is removed but I don’t have space to get my fingers round the plugs so will undo the amp bolts later when it’s hopefully not raining so hard.

Do the plugs have any security, eg tabs that need squeezing from the rear? Looks like the cables don’t have any play and pushing them back isn’t working, cheers.

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Hmmmmm, :thinking: TBH Phil I can’t remember? Knowing Mazda, there’ll be some fiendish security clip that’s impossible to remove :nerd_face:
You may have to remove the amp first, then disconnect. Those sort of plugs do normally have a spring clip that you press in, then pull away from the socket.

Barrie

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Very good info Barrie. I didn’t know it was there either!

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Just had another look at the link I posted from the Bose repair company, have a look and there are details provided for removal :+1:

Barrie

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I thought so, round the back no doubt where very hard to access.
Hopefully there will be an inch or two of play - will let you know later, also if the odd noises have stopped.

Thanks so much for the info!

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Hi Phil, HTH, let’s just hope this is the issue :crossed_fingers: I’m sure that’s the problem though, first time that mine ‘popped’ it frightened the life out of me! :smile:

Barrie

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It sounds like when I leave my Dad’s house and he knocks on the roof!

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Ok, thank you very much, that seems to have worked! The plugs were a bit tricky to get out because of tight access. The security tabs needed pushing in and the only way I could pull the plugs was to not care if I damaged the wires but by that stage I didn’t!

Just ran the engine for 5m and no popping.

I won’t have it repaired as it’s 10 year old tech so might as well have DAB. Is it the case that the speaker cables are reusable and will connect to the next head unit? Tweeters and woofers in the door? If so then I’ll go shopping :slight_smile:

Thanks again, hopefully this is also what was draining my battery.

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Hi Phil, glad that cause was identified :+1:Now, what i did was to put 8" alpine component speakers into the doors as direct replacements for the big Bose ones. Didn’t attempt change any other ones but they sound great! The thing is, I believe the head unit outputs go back to the amp and then speaker outputs go from the amp? By disconnecting the amp, no speakers will work without tracing wires back to the amp etc. For a non electrical guy like me, that was too much to try and fathom so I routed cables direct from head unit into the doors. Bit awkward as there is a ‘cranked’ multi connector into the doors for other things as well, but do able, obviously by direct connections. Have fun!
Barrie

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Thanks Barrie! Awesome assistance :slight_smile: