So for quite some time, I have been hearing a very quiet sound on the Disco, noticeable mostly when sitting at traffic lights as it's so quiet that you can't hear it otherwise... anyway, it sounds a bit like a quiet clicking associated with injectors firing, not valve train related. Here's the kicker... it's not related to the RPM the motor is spinning at (which rules out the injectors as the source).... motor is spinning at 800 ish rpm, and the clicking basically keeps time... then for no reason, doubles in frequency... (RPM still at 800).... Sounds like some kind of electrical relay, not necessarily mechanical.

I have 67K on the rover. Did the 60K service as per Disco Mike, flushed with ATF, run Mobil 1 Synthetic, etc.

Any ideas? Anyone run into this? Like I said, you can barely even hear it, but more curious really than anything...

 

Next time it does it turn off everything, your stereo, HVAC, everything and see it if still does it.
You may need to open the hood and poke around.