Hi,
        I hear a jet engine sound under moderate to heavy acceleration, from
under the car ( 85 Chevy Caprice 305 with 358K miles).  Just before this noise
started, I  had a new Maremont muffler and new tailpipe installed. Also, the
mech shoved the
driveshaft around ( to left and right) to show me that the trans mount was
loose. Trans mount is not moving up and down, just left and right. Trans mount
is only 1 year old.

       You have to roll the windows down to hear the noise. It bounces off
buildings and other cars. Sounds sort of like sand blasting, and also the loud
rushing wind sound from a bus taking off from a bus stop.

    Car does not make the noise when I rev the engine in Park. Also no noise
when car is coasting.

 My ideas so far   :

 1.    Maremont mufflers make that sound.   :(

 2.     Trans is making the noise.

 3.    U joint is making the noise because the driveshaft has moved due to
loose trans  mount. ( U joint only 2 years old).

 4.  Timing chain starting to rub on oil pan !  :(

What do you guys think ?

Thanks