A  few months ago the radio in the van has developed a whine when
engine running. You know, increasing frequency with engine speed, and
no whine at all when engine off. It's present on all inputs: tuner,
cd, aux, usb.

Came on all of a sudden, and only on the front speakers which are
powered by separate amp and go through crossovers.

What I have done:

-redid all grounds, signal, and power leads to front speakers,
crossovers, and amp - no change
-swapped in another amp - no change
- tried alternate pair of rca jacked leads from head unit to amp,
straight run, not crossing power lines - no change
- new antenna and lead to head unit (old one was really bad at head
unit) - no change
- if i grounded amp directly to battery post instead of body, noise
was louder. BTW, the amp ground wires are a short run twisted trio.

Recently the noise has become louder and worse.

Today I pulled the alternator and:

-pulled brush pack and cleaned connections
-pulled the noise reducing caps on alternator and cleaned connections
-removed the diagnostic plug (TDC sensor lead and plug) from alternator
-pulled distributor cap and cleaned, above and below black plastic
shield
-cleaned up edge of rotor
-cleaned all the grounding points (pivot bolt area etc) on alt body

these things have improved things, the whine is much quieter.

Can anyone suggest anything else?

thanks

alistair