Electrical -- thumping in tail???
 

2001 986.
While stopped in a parking lot ...... parking lights already on........switched on headlights and heard a rapid thumping sound in the tail end. Beats were 2-4 per second and fairly loud...enough to scare the heck out of me. It stopped when I turned the headlights switch off. I then shut the car down and looked out back to see if the spoiler had done something funky. All looked normal and the spoiler operated manually as it should. I restarted, turned on the headlights and all was well again.
The problem has occurred a few more times in a week. Definitely something in the spoiler mechanism.
I have been having a strange problem that is probably related after installing an HID kit 10 mo ago I have my oil and batt idiot lights coming on when headlights are switched on (covered in another post). This appears to be related as it is initiated when the headlights are switched on.
I'm going to undo the HID kit and se if the problems stop, but any advice would be greatly appreciated.
Thanks, Bob

it sounds like uncommanded relay engagement. you probably have part of the HID unit hooked up to something that draws current through the pulldown coil of the spoiler relay. once sufficient current flows through the coil, the e-mag force is enough to trigger the relay.

who hooked up the HID kit? was it a direct plug-in, or is it wired into the fuse panel somehow? what other aftermarket equipment do you have?

I did the HID install last winter. Direct plug-in type. No other aftermarket electrical stuff. Right after installing I had the idiot light problem. The vendor said that he should have provided some in-line capacitors for the HID being that this is a Porsche, so he sent them, I installed, but no change. But the somehow related thump thing just started last week.

I like the sound of your suspician, but don't understand it too well yet.

Bob

Likely a good call on the relay. If you can repeat the problem, open the trunk and access the rear relay panel and see if you can hear, or feel, the realy which is trying to activate. Not necessarily the spoiler, I think you're seeing it as such because of it's location in the rear. But a relay working could be amplified by the panel in the trunk

Thanks for that idea, but keep in mind that the relay or what ever it is is only a symptom of some electrical malfunction. I did place my hand on the covering in the trunk below the spoiler while it was thumping, and on the spoiler itself, and feel a light vibration. I know the relays are along the inner left fender, but that is not where the noise sems to be coming from. I'm thinking a relay induced mechanical noise in the spoiler mechanism. But again this is only a symptom of a problem that has to do with drawing power at the headlights.
Bob