Humming noise in cabin.

[Skaanning]

Hi all,
I am look8ng for help and advice with the following problem. Problems quite similar to mine has been discussed in other threads, but in my case things are a bit different.
I have asked a very knoweledgeable friend in the US who has been very helpful in other cases. As a start he suggests to check the switches one by one to narrow down the problem. I will do that, but I would like to know if others has had the same problem.
Here it goes...
A few days ago the battery was flat. Can't say why as the battery is quite new and has no issues. After charging the car a humming/buzzing noise has appeared. No matter whar I do it remains. For 3 days now. Engine on or off, key in or out - no difference. Only when I disconnect the battery it stops. So I guess it must be some electrical part.
The sound seems to come from the right part of the dash. Or maybe atound the aircon. But sounds are tricky...
At the same time as the noise began another odd thing happend. The light in the light switch for the headlamps are on all the time. The light in the actual contact I mean. It is dim and hard to see, but it is on no matter what I do.
Could there be a connection between the 2 problems? Any idea for a fix?
The car, a 1998 Boxster 2.5, is otherwise in very good sharpe with no electrical issues.
Any help is very welcome!
Lars, Denmark

[Fiddlebog]

When it comes to buzzing it can be so many things. It could be a jammed fan, a faulty relay, sounds system feedback, etc. If you could provide a video with the sound, that would be helpful.
I'm also not sure what you mean by the switch for the headlamps. Could you elaborate/provide a photo?
Also: a tip for isolating sound locations: Get a long screwdriver(or any other rod-like device) and hold the handle your ear, then place the other end on different parts of your car. Sound travels much more easily through solids than through gasses(air), so when you put the screwdriver on the source, the sound will be much louder through the screwdriver.

But if I had to make some random guess as to what your problem is, I would say you probably have a fault relay. Those things go out pretty often.

Another way you could try isolating the problem source is to pull fuses(make sure you put them back in the right spots) until the sound stops. Then you will know which system the problem lies in.

[dsjwilson]

Another good way to isolate sounds is to use a length of hose. Something with a center opening about 3/4" (2cm) works well. I have found that a 1-1/2 foot, 2 foot length, is good. Put one end to your ear, and move the other end around in the area the noise is coming from. It works amazing well to isolate the location, and help to determine what type of sound it is. Good Luck!

[pomerlo]

First thing I would do is to replace the ignition switch.
These are known to fail and cause many sort of weird problems. Cheap to replace. You can get the instructions here:
Replace Ignition Switch

Good luck

[morgal48]

Consider pulling fuses one by one. If the sound continues with engine off and battery connected, you may have a short to ground. Pulling and replacing each fuse until the buzz stops should isolate the circuit. Once isolated it should be easier to locate.