Put dry ice on the tar, let it sit for a while, and then smack it with a hammer. Hopefully it will break into pieces and release itself from the metal. You can scrape off the remaining chunks with a putty knife ... I got one with a beveled edge from the hardware store that worked great. Once all the big pieces are out, spray all the little left-over pieces with WD-40 ... this will basically disolve the remaining tar. Wipe everything up with paper towels. Spray everything down with Simple Green or glass cleaner to clean up the WD-40 and you're done.

While a bit long, I've found this method to be one of the easiest and cleanest ways to remove the tar/sound deadening.