My 2000 Maxima SE, Manual Trans, has an annoying ticking noise, I
really need some suggestions in diagnosing it because the dealer found
nothing when I took it to them 2 years ago, they said bring it back
when it's permanent, for 18 months it disappeared, but now is back with
a vengeance, although still not permanent.

The noise appears to be coming out of the front center air vent, but a
friend who put his head down in the passenger foot well could hear it
clearly too. When you pop the hood it's not possible to hear from
outside, although you can still hear it inside while the hood is open.

It also seems engine speed related, it's typically only audible above
3000 rpm, and increases in frequency (ticking speed) linearly with
engine speed, e.g. the ticking is twice as fast at 6000 rpm versus 3000
rpm. I think it's something around 100-200 ticks a minute, although
this is somewhat guess work as I haven't measured the ticking
frequency.

It doesn't matter whether you're moving or stationary, whether the
AC is on or not, whether the air flow fan is on or not, whether
you're in gear or not, whether the engine is cold or has been running
for a while. None of these combinations seem to make any difference to
whether you'll hear the noise or not.

Suggestions?

Thanks,
Roland.