He is restless and looking to escape ! That is a very small cage for him , he needs more room. (10) gallons of water alone for every inch of shell is minimum. Maybe fill the 75 gallon to top and DIY "ATBA" may help.
Another idea : Rubbermaid Stock Tanks are cheap but very strong and have a much wider area for turtles. You can also do much more with them to make you turtle happy.
Once I offered a larger home and he loved it all was good ! Just an idea of what you can do :
https://youtu.be/Ca7w2FCMSyIAlso if can answer these questions in some detail may be able to help more :
How big is your turtle?
How long have you had it?
What is the water temperature?
Did you use a thermometer?
Are you using a water heater?
How much water is in there?
Are you using a water conditioner?
Are you using any filtration?
What is the basking temperature?
Is there a basking light?
Is there a basking platform that is easy to climb on?
What kind is it or what is it made out of?
Is there a UVB light?
What have you been trying to feed it?
When was the last time your turtle ate?
How big is the tank/pond/enclosure?
Is the tank near a window?
Is the tank in a room with a lot of activity?
Have you read the Basic Care section?
Have you searched the forums for similar situations?
Is there any other unusual activity/symptoms?