Hi,
I'm not sure what it is but I imagine it's on the tape so getting rid of it will be tricky. It's not rumble, the frequency's too high, and tapes don't suffer from that anyway. Try the hiss filter, see what effect that has, although the result might sound a bit artificial with that level of background noise.
There isn't a way to insert an image directly into a post, no. You have to upload it as an attachment (as you did). It's a limitation of the forum software we use, sorry.