Grinding Noise during acceleration at low speeD?

This is on the fiero but thought I'd see if anyone had any ideas..

Just the other day, she started making a grinding noise during acceleration at lower speeds, 0-30mph it is most noticable. It can happen above 30+mph, but I really need to step on it to make it happen there.

Seems that the slower I accelerate, the worse it is. Once I'm up to highway speeds, its totally gone.

Only happens in forward gears as well, not reverse gears. And totally goes away, regardless of speed, once cruising. Only happens during acceleration.

I haven't had a chance to crawl under her yet due to the rain the past few days, will do though soon as it gets a little dry around here...need to put a new fuel filter on anyway! I already glanced under there though and seen nothing out of place.

Anyone have any ideas?

Also keep in mind, while she is rear wheel drive, she's a mid-engine car, so its a FWD drivetrain in the back. So she has a transaxle and no driveshaft.

Thanks, Stephan