Funny I just replaced my sohw-1693S after number of years of use and many, many hundreds (over a thousand burns for sure) disks. Same thing happened.... a new disk sounded like it was ready to explode out of the burner. I used canned air for to clean it out, helped for a little bit. I eventually just replaced as it would only burn CDs not DVDs.
Time to replace refu021 as you don't want it to ruin recorded disks.