I don't often stray onto the cat board but this one caught my attention.

If I am understanding the situation correctly you have two adult, indoor, cats that have started to show this behaviour recently?

If this is the case then your cats are showing classic displacement behaviour. They are not able to express their natural behaviours or personalties in the environment they are living in. They have, therefore, turned to an activity that they have control over, that gives a physical sensation which overtakes the mental stress, that gives focus and purpose to their lives and that is a variant on a natural behaviour - this releases endorphines which are painkillers - so, again, relieving the mental stress. This behaviour will quickly become habit as it is the only activity the cats have to find relief and that make themselves feel better.
New toys will not stop them unless they are challenging toys or mega-toys - like ledges and carpet on a wall in a room that the cats only have access to when you are out. Their favourite toys, in rotation, can be left on the ledges and shelves for them to discover.
Give them height, give them carpet, give them rope - anything they enjoy and lots of attention when you are home. Access to the fun room should only be when you are not at home.
Building an outdoor enclosure would also be a great thing for your cats - with access only when you are not home.
Hope this helps.