Don't quite know how to figure out the 'rate' of it - but I do know it was rather fast. About 160+. That was about the same as my sons as well. 18W4D today so thats not bad going...though perhaps the baby was just in the perfect position for me to hear. I think they are floating up high in my uterus (sideways with feet dangling down) at the moment based on where I feel movments.
Have been recording all sorts of sounds with my 'electronic pinard' (lol) - But have yet to figure out how to 'share' it with the world yet! Think I need to try another program in recording it. Hope to get them up soon though - so far I have some good 'kicking' ones where baby is doing a little dance...not to record this heartbeat! :D