I'm just curious as to what could be causing an odd noise in my XJ8 base. It is kind of a "crunching" that sounds as though it's coming from behind the two middle vents. Also, it's not continuous in that, while it's happening, the interval is something random like a half second of noise, stops for one second, happens again for one second, off for a half second, etc... The weirdest part is that it not only happens when I'm driving, but it also continues for several minutes even after I turn off the car.

I thought maybe it had something to do with the A/C, but I've been driving around with out the A/C or the blower lately and it's still happening. I haven't owned the car all that long, but it's done it the whole time. Any ideas where the noise might be coming from?

 

Mine does it too after turning the car off.

 

Not sure it's the same sound - but my 2008 VDP is making a faint, irregular bzzt bzzt sound while driving - a bit like some corny "robot motor" movie sound effect.

Not exactly middle vents, but maybe closer to center console or rear seats... not related to anything I can control (AC, fan, windows, ...).

Eventually I settled on believing it's the fuel pump.

 

Oh, I re-read your post... it's obvious what causes your half-second on, half-second off noise!
It's the dashboard clock!

...

When I got my VDP new, I was amazed how the car is so quiet, you can hear the clock ticking...

 

The noises behind the dash are most often coming from the small climate control aspirator fan (mounted behind a small grille near the steering column); this fan starts operating when the driver's door is opened and continues in operation for some time after the engine is shut off. The fans suck air through the grille - and eventually the fan gets quite dirty, and the result is noise. The fan unit can be cleaned, and this usually quietens the fan operation.

 

I've only had my XJ8 for 6 months, but it makes a continuous clicking noise - finally figured out I must have a broken part within the vent controls. It's not the clock, its part of the servos that control the ductwork (which vent is open or closed, etc).
Fix is to tear apart the dash before the associated parts break, but I'm putting it off as I'm afraid to pull apart the dash. Will have to face up to it sooner or later.

 

You may be onto something here. I did a little more Googling on this. While the noise and location aren't exactly what I'm hearing, the timing of it sounds like it most certainly could be the problem.