I put in a poly transmission mount yesterday, now my car is rattling pretty bad. Is it possible for the vibrations to set off the SES light? (I'm going to get a stock tranny mount and ditch the pos polly mount)

 

leave the mount in & just go get your car scanned......it's something else

 

Not likely that it caused the SES.

 

Well it is too much of a coincidence that it came on a day after I put the mount in, and it is vibrating pretty bad, so I think its getting alot of false knock or something...

 

Knock, false or not, does not cause the SES, though.

Unless your vibration caused something to fall off....

 

I would get your car scanned if I were you. Go to Autozone. They will let yoiu scan it for free. Do it in their parking lot. Write down the entire description and come back to this post, we'll help you out.
Coincidences do happen after you change something.
Example:
When I put in headers, my SES light went off twp days later. I was like WTF? I scanned it and the scanner said that I had a bad 02, Well I didn't want to believe it. Before I was about to buy an 02, I thought I'd check down below. I checked it out and everything was fine. I unplugged the 02 and then plugged it in again, even disconnected the battery to reset the PCM. Well, SES still on and a week later I checked and saw that my Airpump was disconnected. I must of forgotten to hook it back up from when I did my Opti at the same time as header. I plugged the sucker and reset the PCM and "walla" the SES light went out & has remained out ever since. See..I almost had to spend $90 for a new sensor when I didnt have to...Sometimes these things happen...so get it scanned....and look at everything associated to the problem