When searching for a game disc on ebay, I noticed some of the listings say PAL, and others say NTSC. In regards to this game, is there any distinct differences between versions?

I cant tell, although I have never seen an NTSC version of DiRT 3 whether it be youtube or irl. In case if you wanted some footage to analyse the differences yourself since I am unable to, you could use my channel as a source of PAL gameplay https://www.youtube.com/channel/UCkSG83ov82RoP-RN1cXiQZw/featured