I changed the filter and fluid in my 3-speed about two weeks ago. When I first started driving it, I noticed the shifting was much, much smoother. Then about 10 miles later, this strange sound began whenever I hit the gas. The fluid level was fine. It reminds me of the sound coming from the steering column area when the ABS kicks in. When I first heard it, it sounded like the filter was loose and banging around the inside of the pan. But it dosen't always make that sound. I'm at a loss for what it could be. Hopefully it isn't something from the engine itself. Any one have any ideas? Thanks.

car has 82,000 miles