General Maintenance & Repairs - Grinding when in D"" during cold idles and acceleration

Ive searched and searched for topics related to "grinding" and they all sound KIND of appropriate to my situation, but are either too vague or not quite what my situation is, so hopefully I can get some help:

The car is a 98 TA with Pacesetters and a straight pipe. Thats the only modification to the car.

On a cold start, when I put the car into Drive, I'll hear a low grinding coming from what FEELS like right under my feet (where the driver side longtube is). Under cold acceleration, it continues to grind a bit, and I hear considerably worse grinding at cold idle.

After I drive the car for a bit, the "grinding" begins to feel more like fast vibrations coming from under my feet, and becomes much less audible. The sound/feeling at idle completely goes away at idle after the car's warmed up: The ONLY time it grinds/vibrates is under acceleration.

It's not a "clunk" or "bang" so I don't think its the tranny mount. I don't think it's a bad U joint so it happens at idle, so I'm thinking it must be something with the transmission, right? Internal perhaps? I have no idea. ANY help would be great. Thanks everyone!

Check to make sure it's not rubbing against the steering column. When I had pacesetter's on it would rub up against them.
Just a guess.

This might be dense of me, but where would the Pacesetters even have an opportunity to rub on the steering column? I cant imagine how they'd be routed in such a way to brush up against it. You aren't talking about like, them brushing against the steering rack, are you?

This might be dense of me, but where would the Pacesetters even have an opportunity to rub on the steering column? I cant imagine how they'd be routed in such a way to brush up against it. You aren't talking about like, them brushing against the steering rack, are you?

No. The linkage that connects the steering rack to the firewall (steering colummn in the car. Depending on type and maybe the condition of your motor mounts the space between the headers and this linkage can be very very close if not touching.