'86 Toyota truck squeals when cold; only when driving

I just acquired this truck from my parents with an actual 50k miles.
It's a 2wd extra cab SR5. It seems fine except for an odd squeal while
driving when the engine is cold. The sound isn't subtle. It is a fairly
high-pitched whine or squeal that warbles slightly at the frequency of
the driveshaft (I'm guessing). I can change it's tone and loudness by
varying the throttle... no noise when coasting. If I start the truck
and let it warm up for ~10 minutes, it doesn't make the noise at all...
normally it takes 2 or 3 miles for it to quiet down.

Any ideas? It doesn't make sense to me. If it was a belt or something
in the engine, it should make noise even when I'm not driving it. On
the other hand I don't understand why warming up the engine would
silence the drivetrain.

Thanks...

In article <1167457132.076981.248410 RemoveThis @a3g2000cwd.googlegroups.com>,
rruffrruff RemoveThis @yahoo.com wrote:

> I just acquired this truck from my parents with an actual 50k miles.
> It's a 2wd extra cab SR5. It seems fine except for an odd squeal while
> driving when the engine is cold. The sound isn't subtle. It is a fairly
> high-pitched whine or squeal that warbles slightly at the frequency of
> the driveshaft (I'm guessing). I can change it's tone and loudness by
> varying the throttle... no noise when coasting. If I start the truck
> and let it warm up for ~10 minutes, it doesn't make the noise at all...
> normally it takes 2 or 3 miles for it to quiet down.
>
> Any ideas? It doesn't make sense to me. If it was a belt or something
> in the engine, it should make noise even when I'm not driving it. On
> the other hand I don't understand why warming up the engine would
> silence the drivetrain.
>
> Thanks...

Belt squeel.
Try replacing the drive belts.
There are 2, they cost under $10 each.
If the belts don't fix the squeel, it can be the idler bearing on the
upper belt tensioner.