Toilet not refilling properly

A few months ago my Dad and I installed a Toto Drake toilet in my house. Recently, when it is flushed and begins to refill, the flow of water keeps stopping and re-starting. This continues until the bowl/tank is filled. Sometimes if the faucet at the bathroom sink is turned on full blast while the toilet is refilling then the waterflow to the toilet will continue without the stopping and starting. I've checked the hoses inside the tank and can find no blockages or kinks. Any ideas on what the problem is and what should I do to fix it. Any help is greatly appreciated!

 

It is most likely the washer inside the shutoff where the supply line is attatched. Try replacing it.