Thanks, everyone, for suggestions for what to look for. I'll compile
them and take them with me next time I see the mechanic. There might be
something there that he didn't think to look at.

--
Rocky J Squirrel

On Sun, 2011-04-03 at 09:54 -0400, Jim Johnston wrote:

> Not sure if it was mentioned yet, I suggest checking each rear shock
> by grabbing and trying to twist it.  You may hear a what your looking
> for...
>
>
>
> I had a rear shock with loose top bolt make the sort of sound you
> describe...
>
>
>
> Jim
> Wilmington, NC
>
>
>
> On Sat, Apr 2, 2011 at 3:50 PM, Rocket J Squirrel
> <camping.elliott@gmail.com> wrote:
>
>         The thunking only occurs when the drivetrain gets slack. Like
>         taking
>         your foot off the gas pedal while cruising slowly on a flat
>         street.
>         Re-applying pressure on the pedal does not cause the noises.
>         Sometimes
>         when the van is moving at just the right speed . . . 8 mph or
>         so . . .
>         on a flat street, sort of idling along, you can hear the
>         mystery thunker
>         going thunk thunk thunk. It's a heavy sound, can be felt a
>         little bit.
>
>         Second gear seems to be perfect to set up the right
>         relationship between
>         engine power and van moving resistance, allows the right
>         amount of
>         slack. If that makes any sense at all, first is too "tight"
>         and 3rd,
>         well, there's a lot more road noise when up in third it might
>         be
>         happening but can't hear it.
>
>         If this sounds like a suspension bushing thing, then we'll
>         look again
>         there. But it feels like a drivetrain thing. But the engine
>         does not
>         move visibly when thunking, the transmission and diff were
>         rebuilt and
>         the noise was happening before and now after the rebuild, and
>         Gary just
>         checked the axles.
>
>         It baffles science.
>         --
>         Rocky J Squirrel
>
>
>
>
>         On Sat, 2011-04-02 at 09:34 -0700, Don Hanson wrote:
>
>         >
>         >
>         >
>         > On Sat, Apr 2, 2011 at 9:10 AM, Rocket J Squirrel
>         > <camping.elliott@gmail.com> wrote:
>         >
>         >         I took Mellow Yellow to see a new doctor . . . I
>         mean mechanic
>         >         yesterday. There has been this mysterious "thunk"
>         sound
>         >         whenever I'm
>         >         cruising at low speeds on flat surface streets and
>         take my
>         >         foot off the
>         >         accelerator.
>         >
>         >
>
>
>         >   Suspension bushing(s) maybe?
>
>
>