Normal? Maybe not expected or usual to hear such popping and crackling, but certainly not unheard of with old audio gear. Can it be fixed? Can the engine or transmission or brakes in your old classic car be fixed? Of course. The only questions are who can do the repair and how much it will cost.
I apprehended you are a neophyte (your post count (4) and "New Member" status kinda gave you away), so I made the (reasonable?) assumption that you were not considering attempting to diagnose and repair the unit yourself. Thus, you would have to seek out the services of a professional audio technician who would offer to provide, for different prices, various levels of service from which you can choose. One of those service levels is a "restoration" which includes extensive rehabilitation of the unit and would certainly address the specific deficiency you describe. Restorations are time-consuming and involve the replacement of many electronic components as well as much measuring and adjustment of operating voltages and tuning of various components. For these reasons, it is quite expensive and must be justified by the value of the restored unit. You don't do a $400 restoration on a receiver that will only be worth $75 when you're finished.
I would advise you to drop the issue of restoration entirely, at least until you're a bit more experienced with vintage gear. Search out a competent tech in your area and engage him to evaluate, diagnose, estimate, and then, if it makes financial sense, to repair your unit. You should end up with a working unit at a reasonable cost that will allow you to explore further what vintage audio has to offer. Good luck and have fun!
