I will try to help you with this question.
The "hissing " noise you hear is probably a high voltage leak.
This is caused most of the time by a crack into the flyback transformer insulation(not repairable to a reliable condition)=this flyback transformer will need probably to be replaced.
There are also other possible causes for this issue,but a defective flyback transformer is one of the most common occurrence.
The problem is,there are not too many parts available for these CRT tvs,it will be pretty hard to find a replacement flyback.
The cost of the part should not exceed -$50-$70,but the labor fee can be as high as -$150-$200.
This is a soldered in part,and the repair is reserved to very experienced technicians(component level repair).
As you can see,the cost of the repair,will exceed the value of a new tv set.
I would not recommend to repair this tv set, unless you have extensive electronic knowledge ,and will be able to repair the tv yourself(saving the labor fee money).
I am sorry for the bad news,but nowadays,it is very expensive to repair the CRT tvs,when all the new LCD and plasma tvs prices are dropping every day!
I hope this will at least help you to make an informed decision about this tv set.
Please,accept my answer only if you are satisfied ,and will be able to leave a positive feedback.
Also,please feel free to ask me any additional,related questions,I will gladly help you.
Thank you so much and have a great day!