2001 Lexus IS 300 Swishing Sound

My car's tempeture gauge will start to go up now and again past the normal temp. The only way to make it go back down is to make a sharp turn or hit a bump in the road. When I do this I can hear a swishing sound of liquid from inside the car and the tempeture goes back to normal. I'm thinking it's a partial block in the cooling system but not sure if or how I can fix it. Please advise.