I have also noticed this too, however I can also see situations where legitimate users might want to post a link to their soundcloud account, or something similar. Perhaps only users with art submissions, or users who have posted a minimum amount of non-spam-flagged comments should be allowed to post external links at all? Or all of their link-containing posts could require moderator approval before showing up.

Maybe that is overkill though - It seems like only ~3-5 spam posts / day. Certainly the "buy soundcloud likes" links and variations are always spam.

I don't mind people having a link to something in their posts as long as their post is relevant to the topic. This doesn't include the generic stuff like "Great post! thanks for this. I will use artwork during my lifetime! I like games. Click my link -> mega shoe sale!"

Not sure how useful my "flag as spam" efforts are, if moderators aren't paying attention to them.

You'd think.  I used a google search of the site to root out a lot of the backlog, but it's not all soundcloud.  There are plenty of other similar like-adding services that are offered (twitter etc).  I think soundcloud might just be more likely to get through because of the number of legit soundcloud links on the site?

Yeah, we really can't block soundcloud links.  There are too many legit music and sfx folks who have soundcloud pages.