nk993

Hello,

I purchased the M490 rear speakers (carnewal) to install on my non-hifi equipped car. (for background: The head unit is a Becker Grand Prix 7990. I recently purchased the car so I am not aware of anything the prior owners did to it, but I was told by the dealer everything is stock.)

Anyway, after installing the rear speakers (and stupidly putting everything back together again) I turned on the radio and there is a very loud buzzing/hissing noise from the rear speakers. It is there even with no audio being played, and gets worse when any radio/audio is played.

Any idea on what could be the cause? Was there anything special I was supposed to do during install other than unplug the cable from the rear speaker and put it on the new one?

thanks in advance

Meenrod

Does it get worse (go up and down) as you rev the engine?

Potentially there is a grounding issue- are you sure the speakers are sitting in the holes correctly with tabs not touching the metal? From memory the HiFi speakers are bigger and I thought they might need a larger cutout. I could be wrong here though.

I would strip it all back again and re-connect one speaker at a time to see which one is the issue without putting the rear deck back. Double check the connections and clearance.

pp000830

The speaker connections really can't produce the noise you describe. It must be coming from a source amplified by the radio head in a non-premium sound system car.

• Did you disconnect the car battery recently losing your radio channel presents and now your radio is receiving noise because it is not tuned to any channel?
• Does the sound go up and down in volume as you turn the volume ****? If not then it is related to the power amp in the head and may need to be repaired.
• As Meenrod askes above does the sound pitch change with engine speed? If so you may have some sort of grounding issue, but I can't see where it would be if your car is truly stock.
• That begs the question is your car's audio wiring truly stock and unmolested and are all the plugs in the back of the head unit in tight? I would pull the radio out and check the wiring and plugs behind it.
• Was a Becker Grand Prix 7990 ever offered as an option on a 993 or did the previous owner or dealer put it in? I ask because it is not Porsche branded and is not listed as an option in the "M" listing for our cars. If it came on the car it might be listed on the window sticker if you have one.

Andy

nk993

Thanks for the replies guys.

• It stays the same regardless of revs
• Havent disconnected the battery. But the radio isnt connected to the antenna (broken connector). It was shoddily connected to an ISO connect with electrical tape, so I assume someone had messed around with it and the Becker might not have been stock.
• The buzzing sound is there regardless of radio input, aux input, or telephone input. ( i usually have it on aux)
• I pulled the radio out and checked the speaker plugs, they seem fine to my untrained eyes.
• Sound definitely goes up with volume

So I guess it is either a grounding issue or the Becker is messed up?

If it is a grounding issue, what should I check for. You asked if the tabs arent touching the metal.. Which tabs and which metal? Sorry for the dumb questions.

pp000830

All is not lost yet. Unplug whatever you have attached to the AUX input as it could be an input impedance mismatch, ground or a failed AUX connection making noise.
Sometimes an input is looking for a low impedance input and a high impedance input makes a lot of noise.
If the noise goes away when you unplug the auxiliary input we can discuss how to quiet it down.
Sometimes an input ground is common to the chassis and so common to the Negative ground power wire. Sometimes it is a floating ground and does not share the ground connection to the body of the car the negative ground power wire uses and if grounded to the body makes noise. This can be tested for as to which arrangement quiets things down if a grounding issue is the problem. I was also thinking the reason you began hearing the sound with the new speakers is they could reproduce the signal that was always there where the old ones probably had bad speaker cones and a failed crossover so not much sound came out of them.
Andy

nk993

So quick update on this. I recently got the new PCCM with carplay installed. New front door speakers and sound deadening on the doors as well. And the rear white noise sound is still there........
The guy who installed it said he is confident the speakers are defective, most likely sat on the shelf for the last 20 years and they weren't great quality to begin with.

Should I just return them or any other ideas?

Copperhead37

I would try testing with another speaker. You will have to uninstall the current ones to resolve the issue no matters what. Before returning or purchasing high dollar speakers and putting it all back together I would take to speakers out set them separately on cardboard and test. If the noise is still there then you know they were not shorting out on the metal anywhere. Then I would test a different speaker on before re installing to verify it was in fact a bad speaker issue. Get a speaker from a buddy oreven a small cheap one from wallyworld just to conduct the test. It would been frustrating to return, purchase pay and weight for shipping only to have the same issue.