07 yaris sedan a/t

[Kluak]

I have an 07 Yaris sdean a/t just under 45k miles. When you accelerate there is a running water noise, as though you took a bottle of water and pour it into another one.

Father in law said it was a heater core.

So with winter coming up we had to start using the heater. but the heater blows cold hair.

So question is... what could be the problem? the ac works, the air blows, engine is warm, there is coolant. etc.

so if it is the heater core, how do i replace this? and how hard would it be? and how much?


Thanks.