Ok, now you have given me the info I was looking for. If Spike is half way mechanical, all he has to do is to take the tension lever cover off and under that you will find an aluminum cover. There is a rod that runs under that cover and it goes clear back to the back of the upper arm and pulls on a wedge shaped piece that causes the upper arm to raise and lower. When you turn the tension slider, it is pulling on that rod and in turn the rod pulls on that sliding wedge causing the arm to rise and apply tension. That sliding wedge is either jammed and not returning to it's relaxed position or someone has turned the tension rod in too far which shortens is and causes the wedge to not slide all the way back with releases the upper arm. That's why I mentioned Scrollsaws.com because there is an article relating to how to get rid of a knocking noise that is caused by that rod. There are pics that show everything. It's a 30 minute job to take it apart, determine the problem and put it back together again.. You'll be back in business and that almost new saw will be working fine. I think someone must have applied too much tension at some point or they picked up the saw using the upper arm and it is jammed. Never lift those saws by the upper arm.