I'm getting the whistling noise which goes away with the dipstick pulled. Wondering if I need to replace entire box or I can do with just the valve. Anything goes bad in the box?

 

To avoid being stuck and possibly breaking the tabs off the valve itself, I decided to order entire unit from FCP and was very easy to change. Ensure the traps gasket is properly seated and falls into channel with ease by moving it around till it seats in.