I have 3 toilets in my house. Whenever I flush 2 of the toilets or whenever the washer is filling or draining, the one toilet makes a whistling sound. I have taken the top off and watched as I flush one of the other toilets to see what happens. Nothing really except I will see the water move a little. I also have a terrible odor coming from the sink in the bathroom that backs up to the toilet making a noise. I have been told that the roof vent could be stopped up. Do you agree? I also read on your site that the plumbing might need to be snaked. Is it costly to have the plumbing snaked or the roof vent looked at?

I have taken the top off and watched as I flush one of the other toilets to see what happens. Nothing really except I will see the water move a little. And when the float bobs up and down that's when the ballcock makes a noise, correct? Answer this as I need to know.

I also have a terrible odor coming from the sink in the bathroom that backs up to the toilet making a noise. The two aren't related.
Remove the stopper from your lavatory. Look down in the drain and you will see a rod about 6" down.(see image) Hair hangs up and fermemts on that rod. Fish it out,(ugh!) . Now pour a quart of bleach down the drain and let it set overnight. Next morning,(and this is important)flush it out with a pan of boiling water If you can't pull the stopper out then your stopper has a opening at the base that the rod goes through so that it can't be pulled out. To defeat this and pull the stopper look under the sink and follow the pop up lever down to the rod. You will see a knurled nut. Now push the pop up knob so the stopper is in the up position. While holding the stopper in one hand, slowly back the nut out until it's clear,(You may need to free it with a pair of pliers) Careful! You don't want to pull it all the way out. Now, GENTLY pull back on the rod while pulling upwards on the stopper. As soon as the stopper clears turn the nut back in hand tight or tight enough to hold the plunger rod up. From here on in you will let the stopper ride on top of the rod instead of tying it down. Now take a bent coathanger and fish out any hair that may have hung up on the rod or the trap. After you have cleared out any hair or trash, just drop the stopper back in the drain. When I install a lavatory I never tie down the stopper so that the owner can check the drain without the expense of a service call That should take care of that smelly lavatory. More questions? I'm as close as a click. Good luck TOM